Three mistakes?

[stuartv]

(2) Spread your weights around to reduce the impact of any one equipment malfunction

Or, even better, get your weighting dialed in just right and then evaluate whether you need any ditchable weight at all.

If you are properly weighted, then you will start your dive negative by the weight of the gas you are carrying.

Example: if you are diving with a single AL80, that tank will hold approximately 6# of gas when it's full. So, you should start the dive 6# negative. That way, if you get to the end of the dive and your tank is almost empty, you will be neutral (with an empty BCD).

If you start with an AL100 (aluminum) or HP100 (steel), which holds about 8# of gas, you'll be 8# negative (if properly weighted). With an HP120, you'd be about 9.5# negative. And so forth.

Your worst case (when using a wetsuit* vs a drysuit), then (when properly weighted), would be if you're wearing a thick wetsuit and you get to your max depth at the start of your dive. At that point, you'll be negative by 6 # (or however much gas you're carrying) plus an additional amount negative for the buoyancy lost from your suit's compression at depth. That might be, say, another 10 #.

If you get to the bottom, at the start of your dive, and you're, say, 20# negative, total, and you pull the inflator elbow off your BCD and lose all your lift, you will have to swim up to the surface against 20#. And the 20# will get less and less as you ascend and your wetsuit uncompresses. Swimming up 20# ought to be doable for most any reasonably fit diver. And if you're using a thinner wetsuit, you'll be even less negatively buoyant at the bottom. So, for diving in a 3mm or a rash guard, swimming up without ditching weight should be easy for just about anyone.

So.... you can evaluate all this and decide for yourself how much, if any, of your weight needs to be ditchable. But, keep in mind that the most important of all this is that you be correctly weighted from the start. Every pound of unnecessary weight that you are carrying is an extra pound you might have to swim up.

* A drysuit is the same basic story except that it shouldn't be compressing and losing buoyancy at depth. So, with a drysuit, you should be the same amount negative at the bottom as at the surface. And, of course, with a drysuit, if you pull the inflator off your BCD, you can just add air to the drysuit for buoyancy and not have to "swim up" any extra weight.

 

[sunnyboy]

Things I learned over the years:

1. Don't make more than one gear change at a time. Even small changes can become a big nuisance during the dive, but more significant changes (like undergarment) should not be combined with any other change. On the other hand, if you love drama in the dive, by all means make lots of changes each dive. I learned this the hard way.

2. SLOW DOWN. Rushing on land will likely cause you to make a mistake that can ruin your dive or create a "situation" underwater. Rushing to keep up underwater can cause CO2 buildup which is unpleasant at best, and dangerous at worst.

3. Related to #2, never allow people to rush you, assuming you are not glacier slow. Granted, if you are taking 3x longer than everyone else to gear up, maybe do some practice between dives, but if you are in the ballpark, then good buddies will always wait for you. Better to be calm and happy and have a great dive than the alternatives.

 

[Dizzi Lizzi]

I love when I find these little gems!!

1.
3. It is surprisingly easy to change depth fairly significantly without realizing it. Keep a close eye on the gauge and on visual reference points. Pay attention to the particulate matter in the water. If it seems to be going up or down, it means you're going down or up.

Ok 3 mistakes.

1. Diving when tired.
2. Not paying attention to current.
3. Not paying attention to surroundings. I really try to get the big picture now. Nothing like feeling a little lost to start some twinges of anxiety.

 

[SeaHorse81]

I love when I find these little gems!!

Here's another one to go with it, since I notice you're fairly new: those particulates are the secret to buoyancy control. It was only when I learned to notice them and keep an eye on them that I gained decent control of my place in the water column. You get instant feedback on every little vertical deviation as it happens if you're paying attention.

 

[Trailboss123]

1. Descending to depth much too quickly/rapidly almost always contributes to or brings on narcosis much more quickly, in my case. Given that I am one of those people that experiences anxiety when narced vs. a sense of euphoria, it is very noticeable and obvious.

2. Always be careful and double check everything when a well meaning deck hand or DM wants to help me into my gear and take me out of my routine. Twice I have had the dump valve string/bobble thing on my right shoulder get tucked under my shoulder strap unknowingly. Result: the dump valve is held open and and all air in the BC escapes; 5 foot giant stride off the boat and not popping right back up to the surface. You would think that you'd be able to feel or hear well enough to know you aren't fully inflated or hear the air releasing out of the dump valve. But, not so much when in a drysuit and wearing a thick hood.

3. Agree with @sunnyboy - only make one gear change at a time. For a number of reasons.

 

[Hoag]

1. Ignoring that divers a a little like poker players. If they talk things up to make themselves appear strong, then they are probably weak (and vice versa). Be aware of this when you seek advice.

2. Not listening to your "spidey senses". An indescribable "gut feeling" is actually a finely tuned self preservation instinct, and although it may be hard to quantify or explain, it is probably right more than it is wrong.

3. Not recognizing, seeing or reacting to the "3Ds". If you see something that looks Dumb, Dangerous, or Different, then question it. This may be the one thing that breaks the chain of events that lead to a potential accident.

 

[admikar]

(3) When you're new, try not to be the last one in the water. A bit of time floating before the dive gives you extra time to burp your wetsuit, reduce your stress level, and get comfortable, but if you're the last one in the water you add the stress of everyone waiting on you (which you'll probably still feel even if they're actually totally cool with it).

I know there were a couple of significant threads here about staying on topic and all of that, but this is SB, so, what the heck, every thread must go a little bit of and besides I believe that every thread is a learning opportunity.
So...... find new buddies. So far, on most of my dives my buddies were a dive instructor, former military diver with K's of dives and a CMAS 3*, sort of tech diver.
Instructor is patient guy, no rush and all of that. Other buddy not so much.......he starts nagging and cursing......but IT IS ALL BANTER. We are not diving on a clock. TAKE YOUR TIME!

Here's another one to go with it, since I notice you're fairly new: those particulates are the secret to buoyancy control. It was only when I learned to notice them and keep an eye on them that I gained decent control of my place in the water column. You get instant feedback on every little vertical deviation as it happens if you're paying attention.

And that is the main reason that people believe I am competent enough to go with AN/DP at this time in my diving career. Doing deco without visual reference in deep water (as we call it, "in the blue") is no big deal since there is always something suspended in water column

 

[kafkaland]

No problem becomes less underwater.

If it's a minor problem on the surface, it's bound to become a big issue underwater. So if something isn't right while you're still on the boat, be it with your equipment, yourself, or your buddy, don't splash until it's sorted out. And if it can't get sorted out on the surface, bite the bullet and sit out the dive.

 

[Kharon]

Things I learned over the years:

1. Don't make more than one gear change at a time. Even small changes can become a big nuisance during the dive, but more significant changes (like undergarment) should not be combined with any other change.

+1 on this.

Last trip to Bonaire I switched from a BC to a soft backpack and harness no insulation. Got weighted properly and everything was lovely.

Last weekend I dove Lake George with the same rig plus wetsuit/insulation. With the weight on the cam straps (same as Bonaire) I found the tank wanting to roll me over. Who'da thunk? Really sucked. After that dive I moved all the weight pockets (4) to the front straps on the harness.

Sometimes you don't realize that something is an equipment change because different parts of the kit interact differently depending on stuff that isn't intuitively obvious.

 

[84CJ7]

1. Nobody is more qualified to pick out my gear and decide what is best for me than I am, even when I was a brand new diver. Look at the reasons why other people bought what they did and see if they apply to you, don't just buy what they tell you or buy what they use.

2. Commonly taught ways of doing things are not necessarily the best ways.
As an example I was taught to open my tank valve all the way and then close it a quarter turn or some dumb amount. I don't recall the multiple lame excuses for it.
That taught me from experience that if you are stupid (me) you can dive with your tank valve open a quarter turn. Unless you look at the pressure gauge while purging you wont see the drop but the reg will breathe like crap for the whole dive and especially at the end.
Now I open the tank valve all the way and right before I jump in the water I look at the air gauge and hold the purge button for 5 seconds then test breathe both regs for several breaths and fill the bcd until it burps the valve.

3. Don't blindly trust anyone.
Experts are people just as stupid as you are that just have more experience screwing up already, but there are always new mistakes they haven't tried yet.
They also understand and agree with the reasons behind everything they do instead of just repeating the same mindless crap.