"This is my bid, know what i do i aint a kid. I like the offer so dont refuse, i am the guy whom you will again use. Price is good to me, days will go with me." And i won that bid. Not because i rhymed there, but because i was being myself. Client always looks for who is the one out of the way. So i will suggest you to be yourself in your words. Write what you feel. Dont beg or show how good or confident are you. You are already confident enough to place the bid in competition, so no need to tell it. I majorly write my descriptions like that and most of the times i bag the work. So be yourself when you go for it.