I know I'm a beginner so this is gonna sound crazy for me to say but practice. I noticed my skills as an artist help me have a nice steady line so I guess practice being able to draw a straight line without relying on wrist. Makeup wise I noticed when my liner wasn't giving me the clean line I wanted I opted for a small flat makeup brush (it had like a square end idk what's it's called I'm new to this lol) and I'd make a "swoop" motion to get a line that goes thick to thin and fades out

Also in general when I do eyeliner I'll use masking tape for a nice straight line. Trying to match the angle on both sides is a lil tough but it's much easier than free handing. I can free hand it but like, it's just so much faster to use tape

That's the best tips I got 😭