Step 3: Neck Relief and Curvature
Now before we begin we gotta make sure your neck has the right amount of curvature. this is completely preference really, someone who might want to play slide will need more neck curvature then someone who wants to play metal. what most people do to check neck curvature is look from eye level the headstock to the bridge, to get an idea of what the neck curvature looks like. However this isn't very reliable.
One way to measure the amount of relief is to hold down the first and last frets, and to measure the height from the 7th fret. A good/fair amount of height should be around .1 mm to .4 mm.
The second way [the lazy mans way], which is the way I usually do it has basically the same idea as the first way but you measure from the 12th fret., only you don't measure. instead [while holding down the first and last frets] use the thumb of the hand holding down the last fret and tap the string over the twelfth fret. there should be a relatively small gap between the two. If the string touches the fret then the curvature is too straight. Little something i learned from a youtube video sometime ago.