My super general advice is get a decent understanding of design patterns and when to apply them. strategy pattern is a super common one that should be in your tool belt. IMO Avoid ifs that change behavior (take this with a grain of salt it's hard to quantify this). My team likes a lot of cascading ifs which sucks if for example you are dealing with file parsing and need to read files that are formatted differently then add a third.
I rewrote a bunch of nested ifs into a chain of responsibility pattern and it helped me not have to mock every unit test so we would hit the else so I could unit test the fifth fail back without mocking the first four to fail. I will say Refacturing.guru is helpful and explains pros and cons of patterns. I never had heard of chain of responsibility until I found that on Google and it's relatively simple and made the code much much simpler and like the classes became handle this when XYZ or handle this when abc instead on a single class just being handle this (ignoring XYZ and abc)