Try to get at least one thing done per day. Better yet, set aside an hour a day just to work on the project. Don't get too ambitious or you'll never get anything done.
chiming in to say i am considering giving this jam a go too. i have a copy of 2k3, no experience, and no skills but it could still be fun
If it's your first project, definitely look into some free/paid asset packs just to help you along. I know you WANT to do all the graphics/music/sfx/etc yourself, but realistically its just not really gonna happen on a free, month long jam project. There's some great horror assets out there and its not like you're "cheating" just because you chose to use a stock "footsteps on metal surface" sfx instead of teaching yourself how to make sfx when you are trying to learn how to make a whole game on top of that.
Good luck, hope to see your game friend
Get a friend to be your critic, someone who's not afraid to tell you how much you suck.
Or post it here, I'm not afraid to help you with the truth while being as much as a dick as the rules allow me to.