I'm up in New England and catch American Lobster, the one's with the claws. I know nothing about spiny lobster...they are freaky looking.
I'm pretty new at it, but here's my little knowledge.
They hide under rocks, so you need to peek under everything. When you find one that looks legal...it's probably not. "If it isn't scary, it isn't legal." That quote belongs to Spectre and is very true. If you aren't a little bit hesitant about sticking your fingers near it, it isn't legal.
So, now you think you've found a legal sized lobster....poke it in the arse with your tickle stick (a 3 ft long piece of delrin or lucite with a bend on one end) and try to cajole it out of the hole. This takes a lot of patience, as they will try and back further and further into the hole. I've found that if you are making no progress and leave them alone for a few minutes and then come back, it is much easier to get them. Look for "back doors" to their home...try to find where the tail is and poke them from that direction.
Once they are far enough out of the hole to grab, go for it. You want to grab them behind the head, not from the front (at least at first) because those claws don't feel too good on fingers. Plus, if you grab a claw, the lobster, in the interest of self-preservation, will let the claw fall off. Now you have a one-clawed lobster that most likely won't make it another season. It takes a fair amount of time to regrow a claw. AND you can't take the claw.
Once you've caught it, first check for eggs so you don't waste any more time. If it doesn't have eggs, check it's fin for a V-notch (a marked female lobster)...you can't take those either. Then, measure the thing. If it passes all those tests and you haven't dropped it, stick it in your bag and hold the bag away from your body so you don't get nipped by the now very POed lobster inside the bag.
Flounder are easy...either spear them with a Hawaiin sling spear, or just open your bag and let them swim inside.
If you do go diving for lobster, make sure you are familiar with the local laws. New England has some very strict laws with licensing and size limitations.