When you take a shower, do you usually have water pooling up around your feet? It can be quite frustrating, especially if the problem seems to resurface regularly. The first thing that you want to do in that situation is to make sure that your drain is blocking off a lot of the hair and debris that usually will slink down. These things will make a slow-moving drain plug up quickly. It could be that there is a clog forming inside of your pipe. Since these usually build up from soap and hair in the drain, it is tricky to get them moving, but your best bet is to use a snake. They have relatively cheap snakes for home use available, but you could even try dislodging the clog using a wire hanger that is unraveled. It is important that you are careful not to damage the pipes when you do this, however.
It might even work to use a plunger to dislodge the clog, but it is important to remember to plug up the tub overflow tube since you won’t get the pressure needed to dislodge a clog if that is open.