I recently came across a forum post wherein a guitarist resolved to write a riff per day. Not a bad idea. This approach could be adapted for various purposes: One could improvise over a new vamp each day, learn a new lick per day, learn a new song per day; if your practice schedule is light, spread out the new learns to once per week.
But why not go one step further? What you learn, especially in haste for a specific momentary objective, is easily unlearned. I certainly have learned songs and licks a couple of years ago that I don’t even know I have forgotten. What you really want to do is not learn something regularly, but test yourself on a new piece of knowledge regularly.
How is this done? Let’s say you want to learn a new lick once per week. Once you get each new lick under your fingers, practice improvising, making sure to use the lick at every opportunity. If you have cause to write a solo, try to find a place for it. If you teach, teach it.
Likewise, if your goal is to learn a new song once per week, then don’t stop at knowing how to play it. Play along with a recording. Play it in a band. Call it at a jam session. If it’s a jazz tune, write a head using the same changes. Then write one using substitutions.
Take your learning beyond the accumulation of data. Seek to consistently validate and reinforce your knowledge.