I am unemployed, so I have a lot of time, but have a lot of trouble concentrating on my prayers sometimes. It helps to know that God judges our prayers less severely than we ourselves do.
Sometimes it helps to read the Psalms in the Bible. David was subject to depression--a good friend of his, King Saul had become insanely jealous and was trying to kill him. David took all his emotions to God, bad as well as good.
Another psalmist, Asa, wrote a famous passage in the Bible about how wicked people seem to get away with what they are doing. As he wrote the Psalm, he confessed to being in the wrong. It is only when we are not afraid to tell God (and ourselves) how we feel that sinful attitudes can be revealed to us and repented of.