To make it last longer, the acid in the lemon juice helps. Another trick is to strain the pico. Like everyday. The water that accumulates on it will make it go mooshy, but if you are good about removing water it will last a lot longer.
Chopping is the painful part, so I recommend getting a device. I got a $10 chopper at Wal-Mart. Don't pull all the way, or it will break fast.
I like to peel the tomatoes. You don't have to, but I think that's one reason why mine tastes better, longer. An easy way to peel is boil the tomato 30 seconds, and then throw it in icy cold water for a minute and it peels so easy.
Recipe:
3.5 (approx 32 oz) red tomatoes
1 white onion (large)
2 jalapenos - deseed based on tolerance
2 serranos - deseed based on tolerance
8 oz cans of green chiles (I like hot)
10 cilantros, if that makes sense
1.5 tsp of salt (you might want to start with 1 tsp and see if you like it)
lemon juice (start with 10 drops and go from there)
Usually I deseed 1 of each pepper, and I eat pretty spicy.
Not gonna lie, my pico is really good. Sadie's is a really good canned salsa from Albuquerque and I started with their recipe and it evolved from there.