Are they steady all the time or only when the headlights or running lights are on? If it is all the time, then I agree with the above suggestions. A cheap way to check is to turn on the 4 way flashers. If they work, then swap the round flashers on the fuse box. If it is a bad blinker flasher, the blinkers will work and the 4 ways won't. Replacing both is a good idea.
If it only happens with the lights on, then you probably have a bad ground lead inside one or both of the front blinker lights under the head lights. Very common problem. The best fix is to buy a new plug and wire it in. You can though bend the ground tab out a little to make it work. However, for the price new sockets is a better long term solution.