Ok, my method: strip off the old grips by using a Stanley knife hook blade to cut the grip through lengthways and pulling it off.
Clean off any old backing paper/adhesive tape.
Make a quick length measure on the worktop equivalent to two new grips. All lengths of adhesive tape (and backing paper if you want to thicken the grips in any way) can then be easily cut to this correct measure so they won't protrude beyond the grip.
Take a length of adhesive tape, crease it half-way and stick it down the shaft so that the crease is exactly on the butt end. Some spiral it down but I prefer this method and if you measure it first it won't protrude and need trimming afterwards. Obviously backing masking paper, if required, should be layered on in the same fashion before applying the adhesive tape. In an anally retentive way I always rotate the "crease" on the butt end through 90 deg with each layer to maintain an even thickness.
Anyhow, do all the clubs in this way and stack ready for the grips (don't forget to peel off the outer layer of protective paper to reveal the sticky layer). Put the first one butt down in a bucket.
Pour some white spirit in a jug and fill up a grip, keeping your finger over the little hole in the butt end.
Wait a few seconds then release your finger and pour the spirit over the adhesive tape on the club that's in the bucket.
Jam the clubhead into a corner on the floor and slide on the grip. Make sure it's pushed down thoroughly with the heel of your hand and then align correctly, a tiled pattern on the floor is excellent for checking this. Check each time that the grip length is remaining the same as the one's you've just done ie that you haven't overstretched any. If you are unsure about this then keep one club back with the old grip on and check the first one you do against that.
You can keep re-using the white spirit you collect in the bucket by pouring it back in the jug.
Finally, damp a clean cloth or kitchen paper with some clean white spirit and wipe down the shafts for any adhesive that may have leaked down, and leave overnight to dry.
Et Voila !