Here is a snapshot of the tools I will be using as well as the wig that I will be using in this demonstration. As you can see its quite messy.
If you're interested in what type of shampoo I'm using, it's a basic cleansing shampoo. Cost roughly $6 at the local drug store. Any other shampoos should work just fine as well.
If your wig is mildly tangly, I suggest combing it out. Doing so while wet will stretch and damage the fibers of the wig. This is optional. (If your wig is intensely tangled, refer to my other guide).
Fill up the sink with water. Water temperature depends on the type of wig and what you want to do with it. But for now, use a lukewarm temp. Check out the next step for other temps and what they do.
Warm/Hot water: Relaxes the style (only recommended for heat resistant wigs). Cold water: Keeps the original style of the wig maintained (straight, curly, ect).
Pour in shampoo. The amount you use also depends on the length of the wig. Short wigs only need a small amount while longer wigs may use up to a palm-full of shampoo.
Stir the shampoo around and submerge the wig in the water.
Use a gentle scrunching motion to saturate the wig with the soapy water.
It's also good to wash the lace part of the wig cap, especially after a day of wearing it at a convention or around town.
Let's the wig sit in the water for a good 3-5 minutes.
Drain the dirty water and use the same scrunching motions to squeeze out the shampoo.
Allow it to soak in clean water for a minute or so.
Drain the rinsing water and squeeze out as much excess water as you can, as gently as you can. Washing wigs is a delicate process.
Now lay it out on the towel to air dry. Make sure the surface is flat and the wig is out of direct sunlight. If the wig is curly, scrunch the curls up every so often so they don't lose their bounce.
Another way to dry a wig is to leave it on a wig stand and let gravity do its thing. Not recommended for curly wigs, though, as the weight of the water could ruin the curl. Blow drying is not advised.
Once it's dry, just comb out the tangles and wear it to your hearts content! Happy wigging~! :)