I can learn riffs pretty easily, but I have a hard time remembering to work them into my improv. Do you have any good techniques/tips?
The thing for a lot of players is that they'll learn riffs, by copying what's played (obviously!), but not understand where the notes from the riff come from. It may be a riff that uses major pentatonic notes, or minor blues notes, or notes from Mixolydian.
When that's established, the riff should make more sense, and improvising the next few bars at least becomes more straightforward - use the same scale/set of notes to follow! And, more importantly for good improvisation - don't necessarily play a riff exactly as you learned it. Play around with it, play it inside out, backwards, upside down, change the last couple of notes, move the timing, consider different dynamics, etc., etc.
My advice would be too practice the songs/progressions you want to improvise slowly, and as a riff pops into your head, play it. The end goal with improv is for the musical ideas that come into your brain to immediately come out of your instrument, so start by slowing the tempo. Play along at this slow tempo, and when you feel the riff should be inserted, let it fly!
The main thing with improv is not to overthink. As you do the above at a leisurely pace, you'll start to get used to hearing the riff in your head at certain points and it will naturally come out. You'll make mistakes, but just keep playing! When your inner ear gives you the cue to start another riff, launch into it.
Keep going, and eventually you'll develop the spontaneity you're looking for as you get used to this "playing it when you hear it" mentality.
Hope this helps!
A key to practicing anything is isolating the problem that you're having and finding a way to counter the problem. You've isolated that your problem is that you can't seem to work the vocabulary that you're learning into your improv. So spend some time trying to do that explicitly.
Try this. Take a riff, lick, pattern, or whatever that you're learning and try playing only that first. Start by playing the riff instead of improvising. When the chord changes adjust the riff accordingly to fit the changes. Then slowly start changing a note here and there gradually moving on to improvisation. Come back to the original riff occasionally as your theme.
Then move on to another lick and do the same thing. After that try stringing two or more licks together separated by an equal amount of improv between them (ex. 2 bars riff, 2 bars improv, repeat with next riff). Work on both expanding the improv in between and adding more licks in the chain. Also keep working on varying the licks a little each time you play them.
So basically we've built an exercise that does a few things: drills the lick into your head, gives you practice varying a theme, and it gives you practice moving between recalling existing vocab and creating something new.
You could change that exercise as you see fit just remember to narrow your focus to the problem that you're trying to solve and tailor the exercise to fit that.
Also, when it comes to vocab, it's important to just play it a lot. Whether it's a lick or an arpeggio, the more you drill it into your brain, the more likely that musical structure will come to you in the moment when improvising.
After you've taken a lick and you've learned it in every key so comfortably to the point where you can play it in any random key without thinking about it, then take a head that you're learning and literally just force yourself to play that lick wherever it fits. Keep doing that and do just that. Then, start playing filling in the other parts with improvisation, but always hit that lick when it comes time to in the progression.
Also, sing solos. When you sing, sing the lick you're working on. Sing it in the places where it clearly works, sing it in the places where it might not clearly work. Jam the sound of that lick into your ear.
Overtime, it'll naturally start coming out in your playing when you aren't thinking about it. It's a long process, but it's important.
I include melodic patterns in my practice routine and I have found them to help me hear complete melody lines including short licks and other embellishments in my head as I'm improvising on the fly. I practiced scales by themselves and that only got me so far, but when I started practicing the melodic patterns, that's when I started hearing the parts I play and knowing what to play next immediately before I play it. It became an all new ball-game for me.