I echo other comments on the treading. Just like you use your lungs for precision buoyancy while diving, use them at the surface. Try to relax as much as possible.
For the snorkel, I recommend using snorkeling fins. Full-footed or open-heel with no booties. Snorkeling fins are not as stiff. I found that I was slower snorkeling with my scuba fins than when I was actually swimming. Granted, my snorkeling technique has greatly improved since then. Instead of a regular scissor kick, I now use a bicycle kick - bring your leg forward with knee bent and kick the water up and back. This way, you are pushing the water away from you. Before, I was just kicking the surface with my blades. Another option is to frog-kick while snorkeling. This is also a good option if you cramp with your initial kick. Varying kick styles can prolong endurance by working different muscles.
YMMV,
Bri
For the snorkel, I recommend using snorkeling fins. Full-footed or open-heel with no booties. Snorkeling fins are not as stiff. I found that I was slower snorkeling with my scuba fins than when I was actually swimming. Granted, my snorkeling technique has greatly improved since then. Instead of a regular scissor kick, I now use a bicycle kick - bring your leg forward with knee bent and kick the water up and back. This way, you are pushing the water away from you. Before, I was just kicking the surface with my blades. Another option is to frog-kick while snorkeling. This is also a good option if you cramp with your initial kick. Varying kick styles can prolong endurance by working different muscles.
YMMV,
Bri