Blending your bio hair
To begin, you'll need your lace at the temple area cut into the wig hair just a little so that there is no "extra" lace.
Optional: you can use root spray to disguise the lace even more. Carefully cover any lace you don't want to color (like the part that will be over your skin) and blast a couple of sprays on the lace at your temple area. If you mess up you can wash it off and try again.
Next, pull out a thin line of your bio hair so that it hangs down and is not tucked in the wig or wig cap. If your hair has a different texture than your wig (for example, my hair is curly but my wigs are straight) use a flat iron or curling iron on this section of hair to try to match the style or texture. I try to put a slight curl at the end towards the hair so that my bio hair "curls into" the wig hair.
(note: in this picture I am pulling my wig back a little so the lace sticks out and is more visible, but your lace should be laying more flat than this appears)
To blend, take take a wig brush or comb and brush through your bio hair and wig hair so that it all mixes.
You can use this method with any color that is close to your bio hair even if it's not an exact match.
If your wig hair is way off from your bio hair or if you don't have any bio hair to blend, and you have problems getting your lace to lay flat, you may want to use a different method. Instead, try leaving a bit of extra lace (rather than cutting up to or into the hairline) and glue or tape your wig down at the temples.