When I was making my guacamole, I was trying to limit the liquid going into the mixture. I have a tip that I use to keep from getting too much liquid from the tomatoes. This is not a real big deal, but it works.
When you slice your tomatoes, place them on a paper towel. When you cut into the tomato, the paper towel will soak up lots of tomato juice and leave a dry diced tomato. Easy kitchen tip.
Also. notice that my knife is really sharp. It cut through the paper pretty easily. If your knife can’t do this, it is too dull. You need a very sharp knife, especially for tomatoes. Sharpen your knife or buy a very good knife that will do the job. The knife I’m using is a Wusthof Classic, and it retails for around $100. It will last you a lifetime and is worth the money. Keep it sharp with a sharpening steel and you’ll have more fun in the kitchen. Get serious!