Whether you buy a wig for changing up a look or for covering hair loss or alopecia, there are a few things that you definitely need to know before purchasing a wig.

Hair material of the wig

Human hair
Human hair wigs offer limitless styling possibilities just like your own hair. You can color it, perm it, straighten it to make it more natural and more fitful for your lifestyle and need. Without the natural oil from your scalp, it requires more maintenance, styling and upkeep. Thus, it requires you have enough time to care for it. Human hair wigs can last more than a year with proper maintenance.
Synthetic fiber
High quality synthetic wigs resemble human hair wigs a lot. You cannot even tell it is synthetic. A synthetic hair wig is really a ‘shake and go' type and requires less styling than a human hair wig. However, you need to keep it away from heat sources since it will damage the synthetic fiber permanently. Heat sources here includes flat iron, curling iron, hair dryer or any other heat styling tools. Synthetic wigs can last around 6 months with proper care.
Heat resistant synthetic fiber
Some synthetic wigs are made of heat friendly synthetic fiber and they can be applied with heat. You just need to keep the heat below 220F. Thus you can straighten or curl it to change a style. Synthetic wigs are much cheaper than human hair wigs and it usually can last around 6 months with proper care.

Color
Though blonde color is very popular, it might not compliments with your skin tone. You might want to try something different, but it's best to stick to the color that you know is your color.

Size
It is really important to know the circumference of your head before buying a wig whether in a store or online. Take a cloth measuring tape and wrap it around your head. It should start in the middle of your forehead, go down to the base of the skull where the wig will end, and then wrap back up to meet the start of the tape on the forehead.
Different companies or stores have different size banners and you just need to match your measurements with their charts and decide on the wig size.
Take below chart for example, there are 5 measurements that help you decide on the wig size more precisely.

Cap Construction
There are several options for the cap construction including Lace front, Full lace, Glueless full lace, Silk top full lace, and Silk top glueless full lace.
All these cap constructions have a front lace and you need to cut it before installing it. The lace front makes a wig looks more natural and help blend in with your own skin. You can use a little glue or hair gel to the front lace and secure it and make a more natural looking.

If you are not comfortable with using glue, you can choose the glueless lace wig and there are combs, clips and stretch panel for securing the wig.