My tomatoes never seem to do well what can I add to my soil to improve

how many hours of sun and warmth do they get - they need at least 6 hours of sun every day.

Try adding cow manure. Boy does it work great. Add it to all your veggies and floweres. You will have a healthy harvest.

I use coffee grounds and egg shells crumbled. I add to the bottom of the hole before planting and sprinkle on the dirt by each plant.

What do you mean by they don't do well. What do they do? Get your soil tested to see what you are needing to improve your soil. The suggestion about the manure is really good. The crushed egg shells are also a good suggestion as tomatoes need a lot of calcium to prevent blossom end rot. If you are going to use egg shells, crush them up real fine and it won't take so long for the calcium to get into the soil. Use a fertilizer specifically for tomatoes and vegetables.

do get your soil tested. Have a master gardener come out it’s usually free...to evaluate your garden plot. They are a wealth of information.

They make tomato fertilizer spikes that work great for me.

https://www.thespruce.com/top-tomato-growing-tips-1402587