Firstly, you must make sure there is no infection or underlying cause for the crooked toenail, so make a visit to your GP to get it checked. Left for too long, a crooked nail can develop into an ingrowing toenail, but it doesn't sound like that's happened on your case, though it doesn't hurt to make sure.
Let's assume toenail is growing crooked naturally, and you're not accidentally causing it yourself by wearing shoes, socks or tights than apply downward pressure to the toe. There are two options: A naturally remedy, or buying a commercial product.
One of the natural remedies is to cut an inverted triangle in the centre of your toenails. The nail will grow to fill in the gap and will prevent the toenail from ingrowing. Another remedy is to wedge a small amount of cotton under the toenail and to wear scandals for a week or two.
The CurveCorrect Home Treatment Kit
If you'd prefer to buy a commerical product, then a company called CurveCorrect provide a home kit which has won a number of favorable reviews on Amazon.com. The cost is $46.99 from Amazon, or you could or direct from CurveCorrect here.
Here's a short film giving some basic tips on toenail care: