First, for rounding you really should have a truing stand.
Method one. Identify high or low spots.
For a high spot, mark it with tape tighten it and loosen every other spoke. For a loose spot, do the opposite.
Caveat, if your dealing with a really tight wheel you should only loosen things.
This method is more appropriate for a wheel that has lot of hops and flats. Just go along in quarter turns along each spoke. If the spot (according to your gauge) is low, then loosen, if it's high tighten, if it's even leave it along. Keep going around until you get within a millimeter.
After either method, you will have to do some more lateral truing. Than you'll probably have to do a vertical (rounding) true again. Make sure in your final steps that you untwist each spoke by overtwisting it and then bringing it back where you want it.