Preparing proposals and pitching to clients

Hello everyone I do some freelancing work and have a part time job for a medium sized company.

Recently I decided to open my own company but I have never made a proposal neither have I ever pitched to a client.

I have enough budget for ads and have experience in bringing leads in my field but have never done any sales work.

How do I prepare my proposals? Close the deal with client. Some specific way to make the PPT?

Any resources or guide that could help me learn this would be helpful.