A practical guide for Malachain readers, written from everyday experience.
Adults learn instruments well because they practise with intent. Fifteen minutes a day with a clear goal, such as changing cleanly between two chords or playing one scale evenly, beats an hour of noodling at the weekend. Record yourself once a week; the recording hears what the player cannot, and progress that feels invisible day to day is obvious month to month.
Choose songs you actually like, simplified to what you can play now, and learn them completely rather than half-learning twenty. Online lessons cover technique, but a single session with a real teacher every couple of months catches habits early, when they are cheap to fix. Expect a dip in motivation around month three; it passes once the first song sounds like music.
It also helps to talk the subject through with friends or colleagues who have tried something similar. Their experience points out the details that guides leave out: how long things really take, which costs were unexpected, and which shortcuts turned out to be a mistake.
There is more to learn on this subject, and the linked website goes into greater depth. Treat this article as an introduction rather than the final word, and check any important decision against up-to-date, reliable sources before relying on it.
If you try any of these ideas, start small and adjust them to your own situation. What works for one person will not suit everyone, and it is fine to keep only the parts that help. Writing down what you changed, and what happened, makes it much easier to see after a few weeks whether the effort was worthwhile.