First I am assuming that you have a one-piece fence…. If not then you need to buy or make one as it just takes to much effort to set up the two piece type (this is what I had on my first router table and it was a pain),
Actual this is a good question. I have seen people trying to adjust the fence to little marks on the table, a little on this side a little on that side.... For a table saw getting the fence parallel with the blade is a must, however no mater how you turn the fence on a router or drill press you will always be right. You will be at a tangent to the bit, which is what you want. Now that you know that it is very easy to set up a fence even on a less then expensive router table.
The next part of your question depends on what operation you are trying to do. If you want to do a little round over you might just eye ball the fence and tighten it down.
If you want a full profile on a bit with a bearing on top you would want to isolate the bearing. It this case you get the fence in eye ball position then tighten the out-feed side. Using a brass bar (like Rick and Bob) or some other straight edge you put the bar across the bearing and move the in-feed side so the bearing just doesn’t turn as you slide the bar back and forth. Tighten and check again until you’ve got it.
If you were making a cut lets say 1” from the edge with a straight bit, then you would measure from the bit to the fence (if you want the cutter centered on 1” then measure to the center of the bit etc.) Again tighten the out-feed side, measure again and adjust the in feed side to the 1”, when you are on the money tighten the in-feed side. Check again and start routing.
I hope this helped.