The secrets to straight comb, other than the obvious (a comb guide or a starter strip) are correct spacing (the bees space brood 1 1/4" and honey wider) and a straight start. Usually they will follow a guide for the first comb and once they have a straight comb they tend to repeat that. If they do wander it's then an accumulating amount of curve to the comb or a little further over each comb. A spacer will fix the cheating a little every comb, but it's hard to straighten a curved one. Feeding an empty bar between two drawn brood comb is a nice way to get straight comb.
Once they are crooked, then it's a matter of setting it straight again. A straight comb is the best solution. A frame is a way to FORCE a straight comb. If you tie an existing comb in a frame and put it straight in the hive, then they have a "guide" to work from.
Some bees just get a wild hair and go any old way at all.