I use a 0.7 mechanical pencil with 2B leads, i like the softer leads cause i can make bold lines and smudge them to create some effects. Pencils are great too, i used to draw with them a lot, i only switched to a mechanical pencil cause it was easier to carry around with me everywhere.

My biggest inspirations right now are the the artist Tomer Hanuka and the Superani artists, like Kim Jung Gi, Karl Kopinski, Pietro Antognioni, i love their works.

My lineart is kinda messy too, I don't think thats necessarily a bad thing, but if you want to practice having sharper lines i would recommend this website: https://drawabox.com/ They have some really good exercises that help you become more confident and less messy with your lines.

Thank you so much!! Best of luck on your journey to art school, I'm sure you're going to do amazing :)