I just received my new XT crankset. Well done to Merlin and Royal Mail.
Ordered it yesterday at noon and was here today 11:45!
Now I don’t want to **** this pretty ( and expensive ) bit of kit up.
Any advice and tips on fitting this? What are the common mistakes I should try and avoid and where must I take extra care?

If you don’t have access to a torque wrench, do you know what 2.5nm and 15nm feels like? ‘cos they are pretty critical for creak-free performance. And you ought to check it again half way through and after the first ride too. Also I found that my bb creaked aainst my e-type (bb mount) front mech: a bit of grease between the outer face of the bb shell, spacers and cups won’t hurt. Otherwise the shimano instructions are pretty good.

+1

grease the cups, careful with the preload, follow the instructions.

get the frame faced first

don’t forget to get the bottom bracket shell faced as well or you’ll get through bearings pretty quickly

Read the BB cups, put them in the correct sides (they say on them which way they thread in). The frame threads will likely go before the BB ones will

68mm BB shell, frame mounted front mech, no chain device = 1 spacer on non-driveside, 2 on driveside
73mm BB shell, frame mounted fron mech, no chain device = 0 spacer on driveside, 1 on driveside
Add BB mounted front mech or chain device to in place of one BB spacer as required

Insert the BB cups BY HAND until against the frame. Use the tool to torque it then and only then

Cleaning the frame/BB threads and then adding copperslip helps put them in too

dont over do the preload, finger tight is sufficient. Same as a threadless headset, the preload is to take up slock, not to apply any real tension on the bearings.