Petty crime is always there, but you probably already have habits that thwart it like locking your door and taking your laptop to the restroom at the cafe. If a cop catches you smoking a joint on the beach and he happens to care, he'll ask for your cash, but I prefer that to getting caught in the States. ;)
More serious crime is unlikely to target you. Stay out of the north. And you can always live where the wealthier mexicans live in a city if you're nervous.
Quiet towns like a lazy beach town are pretty safe.
I'm currently based in Pto Escondido, a beach town in Oaxaca.
A good way to get your feet wet is to book an airbnb at one of the beach cities you can fly into, take a taxi down a highway that runs parallel to the shore, and get off at any of the smaller beaches/towns for a day trip. You could do a different one every day and get some work done at a cafe/bar on the beach there.
That way, worst case scenario, you're still at the beach with your touristy creature comforts (e.g. easier to find good network if you need to `npm install` -- half-joking!). But if you end up feeling more adventurous, you can take a taxi and find yourself alone on a tiny beach, which as far as I'm concerned, is one of the remaining wonders of the world.
Of course, the hardest part of travel is taking the first step at all. If it wasn't for finding a job in Guadalajara at a small incubator run by an American in /r/IWantOut, I would probably still be miserably working from a Starbucks table in Austin wondering when I'll have the balls to do something new.