To start, the method I recommend is to follow your breath in the way it’s described here: https://www.lionsroar.com/entering-the-jhanas/ – It works for me and others.
Kasinas work for me as well. Self inquiry into the source of “me/I” works very well too.
You should study all of these ways in order to find the one that works for you.
One of the main factors is to have zero expectations and just be without any hopes or desires in order to achieve jhanas. If you try to get it – you will push it away.
It’s much easier with a teacher, but of course you can achieve it yourself as well.
Jhanas is something that’s very natural to all of us.