There is a simple adjustment you can make to hit better slice serves.
Want to know how do do it?
Try pointing your front foot a bit more so that your body faces the net a little more. This will allow you you slice around the ball easier and keep your hips from blocking you when you want to slice.
Don’t worry about your opponents seeing you change your stance. Most likely, they won’t even notice. The focus should be on getting your to hit the slice serve better before you worry as much about disguise.
Check out this video for a detailed demonstration, so you can go try it out on the court.