What is the best way to sell on YouTube ads?

Yes. you can start with audience testing. Start with broader audiences and narrow them down as you gather more data on which segments convert best. You can also create multiple audience segments to test which one resonates most with your ads.

There are entire volumes written on the topic of YouTube
ads, and the type of products that you are selling would
determine the strategy that you use.

I personally avoid watching YouTube ads with the use of
the hyphen, because I'm not going to watch a 2-minute ad
before I watch a 2-minute video, that is a waste of my time,
plus I'm not interested in whatever is being advertised.

I am fairly certain that other users avoid watching ads this
way also, by turning down the volume, or doing something
else in the meanwhile, etc. therefore I am doubtful of the
effectiveness of ads, but that's just my opinion.

I promote products and other things with regular YouTube
videos, I feel that they provide better results than ads, my
videos can be found through searches, but that's just my
own opinion with what I'm doing. Other people may have
a different experience with ads as opposed to organic
videos.

If you would like step-by-step instructions for placing your
ads, details about the structure you are inquiring about,
research results, script-writing assistance, and other help,
I highly recommend ChatGPT or any of the other AI tools.

That is what I use.