Buyers can receive many many Proposals and can't always review them all.
1. To make yours catch the Buyers eye you should first read the Job description so that you know what the Buyer is looking for.
2. Make your Proposal relevant to the Job, do not overwrite, Buyers can be very busy people and do not have time to sift through a mountain of text to get to the desired skills.
3. Consider your Budget. Make sure you sell your skills and yourself. Be confident!
4. Be honest. Don't say you have skills or experience that you don't have. Buyers are here to award you the job because they want it to be completed to their satisfaction.
Once you have completed your Proposal you can offer further information to support your claim via the message board on PPH.