To get your toenails to grow straight try filing them down with a nail file so that they're straight.
Cutting your toenails when they're dry also helps the toenail to grow straighter and be sure to use appropriate toenail clippers and cut the toenails straight across.
And when cutting your toenails be sure to leave them a little long and not cut all the way back.
I've also seen spring clips on ebay that claim to straighten your toenails so that's worth a try if the other above remedies don't work well for you.