Here is my tried and true method. Yes, I also learned many painful lessons in the beginning.
1 - Manscape, you will know if you were not effective at this
2 - Shower the night before rather than first thing in the morning. Your natural body oils will not be enough to cause adhesive failures but will ease in the removal later.
3 - Do not try to remove immediately after the dive. the longer you can wait, the more natural body oils will be produced.
4 - Removal works best if rolled up to remove rather than try to pull off.
5 - Regardless of how good you think your shower and soap is, glue residue will build up on repetitive days and make removal extremely difficult. Use a medical adhesive remover after removal for final cleanup if diving again the next day.
In a bind, you can use industrial adhesive removers too. I have used Goo Gone (with great success) from an auto parts store, but be ready to get your junk in the shower quickly before the burning starts.
Always order one size smaller than the sizing gauge shows. I know this goes against every single natural response from a guy, just order online so you are not embarrassed in front of a teenage sales girl.
ALWAYS dispose of used catheters properly and NEVER leave them on the ground.