Get your financial situation together
Get a pre-approval and/or talk to your banker about writing a letter for proof of funds. (necessary for a cash offer, though sometimes on hi-end purchases you will need to provide both a pre-approval and a proof of funds)
Organize as much cash as is possible—gifts, savings, etc. The more money you can show at the offer, the better chance you’ll have of your offer being accepted. Just because your offer involves financing that will almost certainly be obtained without issue, doesn’t mean that it’s competitive with what other buyers are willing to do.
All things equal, sellers will take more cash every time.