Red is what you are probably doing, green is what you should be doing. I made this in two seconds, so forgive me. This is looking down at the ball.
Basically you want to swing in a path from 7 O'clock to 1 O'clock. 6 to 12 is fine, but most people trying to go 7 to 1, will end up swinging 6-12 anyway.
Keeping your right elbow tucked in on your down-swing helps most people. Closing your stance up will also help, but is more of a band-aid than actually correcting the swing (unless you were open to begin with). You might also try expiramenting with playing the ball further ahead or behind in your stance, and also try expiramenting with a forward press versus none.
One last thing is try taking a 1/2 swing and work your way up to a full swing. If I need to hit straight with my driver (water/OB on either side of the fairway) I'll take about a 3/4 swing right now. It only makes about a 20-30 yard difference in distance (for me anyway) which usually doesn't add up to another stroke for the hole.