Do this, in order. (Each step affects the later ones)
- Using your fingers or a capo, press down on the first fret, and the fret where the neck roughly touches the body. Eyeball how far the lowest or highest string is off the ~7th fret. If there's no gap, slightly loosen the truss rod. if there's more than a tiny gap (Yea, this is vague), tighten it. Only small amounts, e.g. 1/4 turn at a time. Here's the hard part: it may take a few hours or longer before this adjustment settles, so don't get into an oscillation. Warning: Do not force the truss rod if it's resistant to tightening, or adjust it too much without waiting, or you may damage the neck.
- Set the string action lower. Try to keep each saddle roughly level, and consistent action across the strings. How low is to taste; balance the action desired for comfort with how much fret noise etc you get when playing. If you can't get it low enough (Generally on the end strings), and the truss rod is already correct, you will need to do advanced things (i.e. neck shimming), which is out of context for this post.
- Set the intonation: Get all open strings in tune. Measure pitch (tuning) at the 12th fret. If it's high pitch, shorten the string. If it's too low pitch, lengthen. (This is a bit trickier on fretless)
Both the truss rod and action can be checked trivially; you will notice the action immediately, and the truss rod can be visually checked in seconds using the above approach.