What stuff are banks looking for?

I don’t know if this is a stupid question but I will go for it anyway. When banks are looking at transaction and keeping an eye out for problems, fraud, anything illegal, whatever, what types of things are they looking for?

I really just want to know more about this so I’m informed. Also I don’t like feeling scrutinised whether I’m doing anything wrong or not.

Is it multiple payments, multiple recipients, a bunch of transfer in a short time, is it about the amounts, is it the reference or name of the recipient…

If you have an understanding of this, if you can provide relevant information or advice, if you have learnt something through experience, I would be really grateful if you could help me out.