Although not always possible, time is an artists best friend. If you can spare it, put any sketches/plans for your next project away, and revisit them a few months later.
Above, are some rough designs. After putting them away, and moving onto another phase of the project, I recently took another look at them, and will likely make a few small changes. After that, I’ll put them away again, and repeat the process in a couple months. I find this helps a lot.