Great advice from Bruce Foreman

Practice things that are relevant to the music you would normally play or to the work you will be doing. So if you want to play thrash metal, don’t work on your jazz licks. I think it’s also useful to learn things in a similar style even if they are not for performance purposes. So if you’re working on your death metal album, learn some Alexi Laiho solos to help you better your technique and vocabulary in that style.