I used to fly cargo in to Mexico several days a week, been to Las Mochis. Love that part of Mexico; some of the coast there is beautiful. Guymas, about 160 miles north up the coast is prettier, if that's worth anything to you.
The primary deal behind everything going on when you land in Mexico is blowing smoke up the local commandancia's a$$. Be respectful, bring lots of Pesos. If you ask for a reciept you can expect everything to cost about double because then Jorge can't pocket the $$ to pay for sex. The Fox administration was trying to cut down on local pocket-lining with a bunch of posters in airports telling you to please not bribe the officials. Nobody paid them any attention. Almost everywhere I used to go the guy or gal behind the counter where you pay the fees would look at you and ask very suggestively if you wanted a reciept. Just say "esta bien"....and you can save big bucks Or bucks, at least, if that matters to you.
The guy in the flight plan office will correct your mistakes and usually with a smile(because he thinks you're stupid). We kept folders in all our a/c that had our mexican insurance policy, ops specs, and something else I think that I'm forgetting.
Handler.....you give one of these guys a couple hundred bucks and he'll shine your shoes at the end of the day. The few times I used them, usually in Central America or deep into Mexico where my busted-ass spanish wouldn't suffice, they were great. Very hard working guys; you'll get what you're paying for, some of them almost won't let you go to the bano without shaking it off for you.
I think someone already covered it but what the hell: Land, sign the kid with the rifle's sheet of paper, let the dogs on if they bring them, close your flight plan, clear customs. If you're going right back out you can close and refile at the same time then take one of the copies of the flight plan to the fee office and get them working on it all at once while you clear customs.
Don't eat ice, don't drink tap water, don't let the shower spray you in the face, don't brush your teeth with tap water, don't eat veggies with skin(like tomatoes), do try a michelada(again with NO ICE), do have fun. The people are very nice. And it's true, hurrying is an American affliction.