..but it helps to know how old your vehicle is. Sockets can become rusty or corroded with age and just replacing the bulb doesn't help much if the socket is corroded.
Clean the sockets up real well (I shoot some WD40 in there) then use some bulb lube to keep moisture out.
Fast blinking can also be the sign of a faulty ground somewhere in the system, but check the bulbs and sockets first. Good luck with it!
Craig