Personally I always teach the sidepass from the ground before I do it from the saddle.
I put the horse facing a wall or arena fence. I use my dressage whip or my stick to cue with taps. I start by yielding the forequarters a step or two..then the hindquarters.. alternate them so you are sort of see-sawing. Every step, stop, praise, relax. The biggest thing is to get it to one or two CALM steps. If they are running away from you with every step then they wont be ready for you to cue the other end of the body.
Then I start staying closer to the midsection of the horse (not going towards the front for the forequarters or the back for the hind) and I use my dressage whip or carrot stick or whatever you are using and hold it vertically (handle slightly over my head, end hanging down so I can tap lightly..more of a free swinging tap). I tap right at the girth line. If the horse is very new.. I'll tap a little back..and then a little forward.. then right on the girth. Basically you are making the cue as subtle as possible and still being as unambiguous as you can.
When they are sidepassing smoothly I replace my tapping cue with a pressure cue from the flat hand of my hand (at this point using a riding crop can be easier to handle in case you need to go back to a familiar cue).. then from my finger.. then I will tack them up and use the pressure cue from the side of the stirrup.
When they are moving sideways smoothly, move away from your wall or fence. You may have to give a small tap on the leadrope to keep them from walking forward at first. You may even have to go back a couple steps and do a little see-sawing before you have your good sidepass out in the open.
Within 3 days I had my 3yo (who hasnt been backed yet) sidepassing beautifully with light pressure and a clucking sound. In the barn I did find that she sidepasses VERY well going towards her stall..and a little heavier away from her stall

so I just turn her in both directions and go towards her stall so she gets practice on both sides. In the arena it doesnt matter though..haha.
It has become a game at night (well fun for me.. not so much for her).. she comes out and gets groomed before dinner..then in order to get back to her stall for her grain she has to sidepass, back, pivot, square up.. all sorts of things to get in to her stall. She backs like nobodies business through narrow doorways!! Sometimes I set up a row of buckets in the aisle way and she has to back, then sidepass through them.. then back.. then sidepass through them.. then do a pivot on the forehand around the end.. then sidepass to her door.. then I open it.. pivot around so her butt is pointed at the door..then back in the door. Great little schooling session we have every night.. with a reward at the end for her!
I hope I wasnt clear as mud

haha.. good luck