Resources & downloads
If you don't already have an instrument, do RESEARCH and seek ADVICE before you buy. Buy from a good music shop (not via the internet) and if possible take an experienced musician with you.
A vital accessory is some sort of TUNER. The clip-on, chromatic variety is best. It will work on guitar or ukulele and, if you're inexperienced, it will save you hours of grief, frustration and bafflement. New strings stretch and go out of tune as soon as they're tightened up. They'll need tuning and retuning frequently until they settle down. I don't want to alarm you newcomers, but this can take days or even weeks. Having a good tuner makes the process a whole lot easier. These days many people use tuners that comes as smartphone or computer APPS, some of which are FREE, and some instruments now come with built-in tuners.
If the instrument doesn't already come with a BAG or CASE, buy one. They range from elaborate, solid flight cases costing hundreds of pounds to simple canvas or nylon bags, but whatever you buy should be waterproof. If it's padded for a bit more protection, so much the better. At home keep the instrument handy and OUT of its case so it can be grabbed on a whim.
Don't let bad habits get a hold. Unless you're a naturally gifted musician, get some lessons from a GOOD TEACHER (well, I would say that, wouldn't I? - but it's TRUE). Music shops usually have lists of approved teachers. I'm often asked about books. There are hundreds, with so many new ones popping up all the time it's impossible to keep up. If you're having lessons you may not need a book, but for uke players I will mention a goodie I've come across recently:"HOW TO PLAY UKULELE - a Complete Guide for Absolute Beginners" by Ben Parker. I confess I haven't read it cover to cover but what I've seen looks pretty good. I would NOT recommend the more well-known "UKULELE FOR DUMMIES" as it teaches what I consider bad techniques. There's lots of online material and tuition these days of course; some of it is pretty good, but some of it is rubbish - so be careful!
Keep your FINGERNAILS SHORT on your left hand (right hand if you're left-handed). I know Dolly Parton manages to play guitar with long fingernails (not sure how!) but she's the exception that proves the rule.
Be persistent, PRACTISE regularly. Repeat, repeat, repeat. It's repetition that makes it work. Memorise as much as possible or you'll forever be needing to refer to books or bits of paper. The memory is like a muscle: it gets stronger with use.
SING while you play. Some people find it hard to do both at the same time and some people actually don't like singing, or think (often mistakenly) that they can't sing. But uke and guitar are both great accompanying instruments and the sooner you try the sooner you'll get used to it.