I'm just off of work, and having finished my breakfast (dinner?) I'm pretty wiped, so I'll just say it like this.
A good player has to be interested and put forth the requisite effort. If they're not gonna', no offense, but it's better if they don't show up. Don't have time for the game? Don't say you'll join the group. Don't want to play horror? Don't. If you like something, don't be afraid to pitch in! Be thoughtful towards the other player and don't choose options that mess with their fun. Don't try to play 'gotcha' with them or the DM.
If you're there, try to have fun. That helps. If you don't think you will, sit it out. There's plenty of stuff on TV.