Write to Market:
1.) Know your target reader
2.) Use the EXACT channels and methods for that reader

There some channels that work for ALL genres:
-- Amazon Ads
-- Facebook Ads

As a beginner I would concentrate on Amazon ads (they are the fastest and easiest way to learn paid advertising!)

As the other experts have already answered here, your EMAIL list is probably the number one marketing platform available, however, if you are a beginner and have no list...

Go get a list!
Email Promotion Sites are probably the #1 way - especially when you don't have your own list yet.

1.) Know your market/target reader...

For example if you are a non-fiction author who writes about business start ups or similar; then BUCK BOOKS will be a very good email promotion site for you.

BookBub:
"The Mother of all Lists" is an email promotion site, with over 1 million readers. However, they are expensive...
But they serve all genres.

But you should be open and think out of the box at all times.

For example, what if you are a Childrens Book author?

Email list building in this genre is extremely difficult (kids usually don't have emails! So your target reader is NOT your target buyer.)

In this case I recommend INFLUENCER outreach and author outreach. e.g. make Box sets of your books with other compatible authors books!

Networking, and outreach with other authors and influencers is probably the best way of all.

I have interviewed many successful authors on my blog, and most of them say, if they had to do it all over again, they would have started with the networking and outreach FIRST.

It works, regardless of what genre you are in, or what product you sell.