One of the commonly shared basic guides is in the top image on this post:
In short, you want to focus on stacking the strong color against the titan, along with heroes that debuff (decrease) the titan’s defense, and buff your attack. The chart goes into a bit more detail of the breakdown of those categories, along with examples of some heroes.
If you want further specific advice, I encourage you to post your hero roster, so team combinations can be suggested. 