I like to use tomatoes with very little seeds and pulp, if there is a lot of seeds and pulp in your tomatoes discard this and just use the meaty part, you might have to increase the amount of tomatoes.
I use all of the jalapeno (seeds and pigment) because your adding a bit at a time so you can control the amount of heat if you just use the pepper itself you might be running out for more peppers when it is not hot enough!
Avocados need to be in a plastic or glass bowl otherwise they will react with the steel and start to turn brown. VERY IMPORTANT The little piece on the top of the avocado where the stem joins the avocado is hard as a rock and must be removed, if it accidently gets into your guac and someone bites into it they will be loosing a tooth, look at picture no 2. I just cut the surface of the avocado length ways and then turn the avocado till sliced all the way around, then i tap the core with the blade of the knife and twist and it pops right out, to get if off the blade i tap it on the corner of the sink easy!
I mash the avocados till smooth finding all the lighter, harder parts of the avocado. I get the chunky texture from the onions and tomatoes