For legal and other reasons, I can’t read unpublished, unsolicited manuscripts. My best writing advice is: writing is rewriting. Polish, polish, polish your work until it is the best you can do.
Re getting published, I think the best advice I’ve seen is author (and former agent) Nathan Bransford’s essays on Essentials of Publishing, available here. Plus, it’s been so long since I had to look for an agent that I fear I am not the best source how that works these days. But there are new authors being published all the time. Educate yourself on the business (there are tons of resources online).