Firstly, make sure your hair underneath is laying nice and flat in a low bun or under a wig cap (optional).
The wig cap can be adjusted to make it tighter by inserting both the right and left hooks into the slots at the nape of the wig.
See image with label 1 below;
The elastic bands (see image 2) can also be adjusted to make the wig fit tighter.
Put on the wig making sure the wig sits flat around your circumference. The lace around the hairline should always lay flat. Adjust the elastic band if necessary. Then insert the combs at the back into your hair or the straps. (combs are optional) If you find the lace is too light for you, use a slightly dark powder or foundation shade and gently dab where the lace is showing and vice versa if lace is darker. Lastly, you might notice short static hairs on the wig. This is quite common with extensions and wigs. Use a serum or holding spray to tame it down :)