Been riding bikes for 37 years and can do pretty much most maintenance on my bikes without issue (wheel builds excepted).

I have never ever attempted to set up a rear mech or even adjust one. It scares the hell out of me, it’s become an irrational fear. However I’m fed up paying a shop to do it when it needs doing so really need to tackle it myself at last.

Any tips? Is there a fool proof step by step that anyone can recommend?

Look at the park tool website at their guides.

Run the cable through but don’t clamp it. Make sure the cable adjuster on the shifter and/or mech is wound in fully. Adjust the low limit screw so the jockey wheel lines up with the smallest cog. Clamp the cable snug but without moving the mech to do so. Try the first shift, and adjust tension till its clean. The rest should go smoothly, you will have to adjust the other limit screw though..

start with a new inner/outer
a straight mech hangar
a straight mech
working shifters
correct cable routing.

after that there are only a few adjustments.
hi/lo screws, b-tension, cable tension – possibly one at shifter and one at mech, starting with them both at 50%

i do it backwards to rocky^ undertaking the fine tuning between 2nd&3rd largest cogs.

When setting up rear mechs I’ve found that adjusting the b-tension screw makes bugger all difference.

Reading tips on here probably won’t help, so just go through the youtube vids on it. eg
[video]https://youtu.be/CPLiW-0zLa4[/video]

It helps if you’ve got a workstand, but it’s not essential 😀

Get it right, working perfectly then make some stupid needless adjustment that buggers the whole thing up then spend a bout 2hrs pissing about with the limit screws and barrel tensioners to no avail before swearing at it shoving it in the shed and sulking.

b-tension ensures the mech top jockey wheel doesnt hit the cassette.

With the last mech I was replacing I actually found using a third-hand set of pliers to pull the cable through the mech and adjusting the mech position on the fly with the pliers to get the jockey wheel aligned with the relevant cassette sprocket was the quickest and easiest I have done it.

Just as well as the cable adjuster on the frame is awkwardly tight.

I always set both limits before attaching the cable or the chain. Line the low limit as it sits, and I just push the mech out and adjust the high limit until it lines up with the sprocket. Put the chain on, make sure it goes all the way up and down, secure the cable, then all you have to do is adjust the cable tension (if necessary).

It’s getting the chain length righd I struggle with. The old “biggest rings +2” has failed me on a few occasions.

i go big big and mech at very nearly full stretch.

yadda yadda chain growth on a full susser

b-tension ensures the mech top jockey wheel doesnt hit the cassette.

I know what its for.

It’s one of the easiest jobs on a bike. This is my method:

1. Set low limit screw (smallest sprocket) with cable unclamped
2. Adjust barrel adjuster so its screwed all the way in then unscrew one full rotation. Make sure shifter is set to the smallest sprocket. Pull cable taught (don’t over pull)and clamp
3. Set high limit screw
4. Adjust B tension screw
5. Adjust barrel adjuster if required (normally isn’t IME)
6. Ride

If that takes more than a few minutes then youre doing it wrong.