Those mental fillers that need to be dismissed

Sometimes having mental and emotional problems basically sucks.  That is the best way to put it.  I have fears and doubts in my life and often times those are the things that I focus on.  The mental fillers that tend to dominate are those that will keep my self esteem low.  Am I filling out those that are positive?  How do I deal with those negative mental fillers, if I have to even deal with them at all?