1) to make a good villain, give them a good motive. my all time favourite villain, from any movie, book, franchise, anything is; zemo from the MCU. first, he had a good and solid motive for wanting to go after the avengers. he blamed them for the death of his father, son, and wife. now, im not saying do this with your villain but to make them a villain, they have to have a motive for what they do and how they contribute in the story.

2) to make your villain, give them flaws. again, with zemo, his plan failed because he was so blinded by his revenge that he was going to end up giving up his life. his flaw was not being able to let his vengeance go and escape. give something to your villain that is something that will make them slip up. have them be arrogant and cocky, and then let your reader watch them get caught because of that.

3) give them a plan. again (again) with zemo, he was precise with his plan. he knew when to strike, and how. he knew that he could never tear the avengers apart, but he saw through that and, with amazing intelligence, he saw a loophole on how to do it with doing next to nothing. give your villain a plan that is fool proof.

4) what is their purpose? how will this villain help the protagonist grow, change and develop properly? 

5) one of the best things, is having your villain unseen or not detected at first. have a big reveal on who it is, that will get your readers intrigued. 

6) where does your villain end up? will they get a happy ending or a sad one? will they ultimately defeat the hero? will they cower away and leave everyone wondering what happened to them?