A truing stand is the best way to go, but you can adapt if you have some patience.
I bought a couple packs of small alligator clips from Radio Shack.
I put a clip om each spoke near the nipple for ONE side of the wheel, thus 18 clips for a 36 spoke wheel.
I'll turn a nipple and slide the clip toward the axle. Repeat on the opposite sid. Then I'll go 90 degrees from those 2 and repeat. And so on, going evenly.
Since your spokes run at different angles from each side, the nipples WON'T be turned exactly the same amount!!!!
Go in small amounts, like an 1/8 turn and measure the difference before & after.
I'll check lateral true between each step.
I just use a felt tip marker and turn the wheel, so the "high spots" contact the marker and thus get "marked". Usually the ink will wipe off, although with some, you might need alcohol or similar. I'll then "pull" the low spots in the direction I want to go.
You don't even need a ruler. Just use a stick or similar. Place against the rim and mark it with your thumb against the chain stay. Keep your thumb on the stick and check the other side to see if it matches.
I would start by loosening spokes on the first side and then tightening the other vs possibly over tightening.

I'd also read the section about truing at the PARK tool site before you start. It can add a lot of insight!