If this is your first snake, I would either recommend a california king or a rosy boa. Both are great for beginners and will not outgrow your 20 gal. Another possibility is a ball python, but whatever you get make sure you have a tight fitting cover for your tank. Make sure you get a heating pad for one side of the cage and the rest of the decor is up to how much you want to spend. Good Luck!
:i need some advice on what kind of snake to get and what i can get. right now i have a 20L tank and i am gonna get around $130 soon and i want to get a scarlet snake or a boa. :what snakes would be better in this tank? :how much is the least i can spend on a light bedding and decor? :thanx for help