A leaky pipe is more than just a minor nuisance; left untreated, it can cause major water damage from deterioration or mold and mildew. It's definitely you should have looked at sooner rather than later, especially if you notice it's been leaking for a while or is leaking in a dangerous place (next to outlets, behind walls, etc).
Plumbing services providers can respond quickly, but in the meantime, what steps can you take to fix that pipe before they show up?
1. Tighten It
If you can, get close enough to the pipe to see if you can find the source of the leak. In some cases, the leak is caused by a pipe that's either been shaken loose or lost its seal over time. Usually, one tight turn of the wrench may be enough to stop it from leaking entirely; if not, look for other sources of the leak. Even though it's difficult to do, you don't want to overtighten the pipe because you could cross-thread it and require a full pipe replacement instead.
2. Patch It
If the leak is not at a connection point, then you most likely will have to use a temporary solution to keep the pipe to keep it from dripping. How you do that is up to you, but one of the most common ways involves putting a simple patch over it. The process for this is relatively straightforward. First, turn off the main water valve to the pipe, then dry the pipe completely using a towel and file off any sharp edges that are on the pipe and may poke through the patch. Finally, apply the patch to the broken area and secure it in place with a clamp before turning the water back on. If you can't find patches, look also for either epoxy compounds or pipe wraps and sleeves. All of those items do very similar jobs in slightly different ways.
3. Clamp It
If patching it and tightening it are not options, then you can always use a pipe clamp. These are sold at just about any hardware store and can do a good job of holding a pipe together until the plumber arrives. Keep in mind though, this is not usually done for just a simple leak, but more in the event of a pipe that is on the verge of busting. Clamps are not generally well-sealed to keep water from dripping out if it's laid on top of it.