As you must have heard " The First Impression is the last impression". So when you think to get your proposal accepted and you are the one who is grabbing the projects from clients, you must have a cover letter where it gives the best impression of yours to the clients. This will automatically benefit you in the best way it can. Make sure you are impressive in your cover letter with the innovative points you are putting relevant to your technical & other skills.
With dedication and effort, we can really write one such cover letter which is performance base attracting and impressive. But to wrote that there are several facts which you simply can not ignore and you need to find out all the potential things which you possess and which will benefit you in getting the proposals approved by the clients. But making an impressive cover letter is not going to be an easy task. You need to work on it hard as if you are not perfect in creating an impressive cover letter, it may lead you to be in a situation where you will be not getting any kind of proposals approved.