People are going to tell you to never share anything when you move in with someone. My old roommate and I always shared everything and it was never an issue at all. I never even understood why people were so concerned with sharing.
Annnnnd it's because I got lucky and my old roommate and I had the same respect for each other's things.
Really really really don't share things unless you don't care if they are broken or ruined. I am super materialistic - I love everything I buy or receive as a gift. So far my roommate has cut through my only cutting board (gift), broken three measuring spoons (gift), scratched up a sauce pan by stirring with a fork (not a gift), smashed the buttons on my tv and appletv remote to hell, and left tons of water rings on the coffee table.
And if you do decide not to share, commit to not sharing. When my current roommate moved in, she insisted on not sharing by buying her own cups, tupper ware, and silver ware (these things make sense to share imo). But then she would share when it was convenient for her... She used my laundry detergent for the first two weeks she lived with me and then bought her own and never repaid me. She did that with my foil, baggies, lysol wipes, cling wrap, bleach cleaner, etc... All of that stuff is super cheap though so no use complaining. It's the sentiment that bothers me, just commit. It also makes me feel like she's living on top of me instead of with me, but whatever.
Another thing, when you live with someone else, you need to recognize that every person has their own way of doing things. When I wash big dishes, I use my crappy apartment dish washer as a drying rack and leave it open. It's against a wall and totally out of the way, so this shouldn't be an issue (and it never was before), but for some reason my new roommate always closed the dishwasher up when she saw it open. Then I'd forget that there were dishes in there for two weeks. And I had to learn to accept that she likes to open and close doors so that everyone in the entire apartment complex knows when she's going to the bathroom. As long as it's not ruining your life forever, you need to accept that different people have different ways of doing things, even down to how a door is closed.
Finally, it's important to lay out things that might be annoying before your roommate moves in. For example, I warned my roommate that I like to keep the common areas stupidly clean, but that I have no issues being the one to clean because I know I'm obsessive about it. Luckily she's just as obsessive as I am there (if not worse), so it works out. :)