I hook up all the cables, before backing up the toad. That way, there is slack in the Readybrake line, so I don't have to pull on the cable (on toad side) to connect it.
Remember, that when you back the toad up to lock the bars, most of the time only ONE of the two arms is going to lock, not both of them. Only ONCE in the last 3 years, have I ever lined the toad up so perfectly that both bars locked at the same time when backing up the toad.
That being the case, there should still be some slack in the Readybrake cable, even after you back up the toad to lock one of the bars. Once the MH moves forward, the other bar will lock, at which point the slack in the line should be gone (assuming MH and toad are in a straight line).
You really need to have both bars locked in place, and MH and toad in a good straight line, when you adjust that cable. I know that makes it a bit more of a pain, 'cause it means you have to drive the MH forward some before adjusting. However, it is the best way to make sure you get it adjusted right.
Once you get it set right, you should rarely have to make adjustments. With time the cables may stretch a little and need tightening, but not very often.