This is called god-modding or power-playing, and not doing it is harder than it sounds. If you find that you feel like you need the other person's reaction before you can go on, stop, and leave them time to respond. Every description says something about our characters, so don't speak or act for someone else! NPCs, (non-player-characters) are exceptions of course but don't overuse those either. Also remember the rule of "Show, don't tell." Why tell us that you're fearless and deadly, when you can show us that by describing the way you walk, talk and the weapons you carry.