Know the facts, but don't rely on them. People make decisions for emotional reasons just as much as rational ones.
Link your ideas to the priorities of those you are selling to. This allows potential customers to see what's in it for them. If you don't know their priorities, find out. People make decisions for their reasons, not yours.
Talk to the main decision-makers, ideally one-to-one. Ask for their views on your ideas and listen. Show them later how these have been incorporated.
Share the credit. The more it seems that your proposal is widely supported the harder it will be to reject.
Break your argument into bite-size chunks. This allows people to follow at their own pace. If you rush, they are more likely to become lost and may reject your idea rather than admit confusion.
Make all the decisions explicit. Start with the big issue (eg, 'Do you think this is a good idea?') and then work through the other decisions (assuming the answer to the first question is yes).
Offer a range of options. This will give those you are selling to a chance to influence the outcome and so feel part of the solution.
Believe in what you are selling. If you aren't confident, others are unlikely to be.
Don't be fazed by difficult questions. Pause, ask others for their views, if appropriate, or say that you can't answer the question now but will find out and get back to them.
Paint a picture. Describe how great things will be if your ideas are accepted (or the terrible things that might happen if they aren't). The more vivid and personal the picture, the greater your chances of selling the ideas successfully.