One of the many agendas thrown my way when I attended GIT in the 80's was Howard Roberts' Super Chops concept. The deal here is to play over chord progressions of course, but relentlessly with steady streams of eighth or sixteenth notes. No phrasing, no pauses, no "playing like a horn player" - just way too many notes! The course was based on the progressions of well known jazz standards, but it can be adapted to work with anything. Record some sets of changes and give it a whirl. Maybe start with the aforementioned "grab a big ol' handful of G!" approach. But also take some I-IV-V vehicles, and force yourself to play the corresponding major pentatonic scales within ONLY one part of the fingerboard at a time (each of the CAGED chord/scale shapes) and don't connect patterns up the neck, play across the neck (you can mix it up later). Play exclusively with straight eigths, swing eigths, and triplets, and you can mix that up later as well. Try landing squarely on the downbeat for each new chord with the nearest available target tone (can't go wrong with the almighty 3rd interval). If you get good at that, start peppering with the aforementioned chromatic passing tones. Whatever you do, just keep playing with no pauses! As with the scalar drills, follow up by playing more "conversationally" with phrasing and such over same tunes/progressions.
One common mistake that I see quite often is that players only play within the new style that they're interested in at the time. Certainly that needs to happen, but music is music, and in my opinion, improvisation is best realized by coming at it from a variety of angles. I'm not saying work out with Frank Zappa or King Crimson records before the big bluegrass jam - but don't overlook related stuff. I regularly cover "Friend of the Devil" by the Grateful Dead, and I often get into bluegrass mindset when my lead ride rolls around. Students are often intimidated by brisk tempos of bluegrass tunes, and understandably so. Lately, I've been having them work out with the Poison Love record by Buddy Miller. I also use Music From Big Pink by The Band ("Long Black Veil" and "The Weight"), and I use Train a Comin' by Steve Earl a lot as well. These tunes have similar changes but at more comfortable tempos. We can bump tempos up after a while.
Another mistake that I see is when folks get way too hung up on being authentic to the style at hand. To me, the best players have reverence to authenticity, but they do their own thing with it as well. I sometimes hear chicken pickin' Tele players that sound like the bulk of their agenda is working with Brent Mason or Albert Lee videos. Don't get me wrong, those guys are phenomenal and that's gonna promote impressive technique by default. But it ain't gonna build a style. Same deal with the "mathematical" approach of shredheads in the 80's. Instructional DVD's are wonderful, but do your own thing too, and don't get bent out shape worrying too much about authenticity.
Early in my career (?!), I happily and constantly learned new licks and lines, and couldn't wait to superimpose them wherever and whenever I could on the bandstand. After a point I realized that this could sound trite and forced - the musical equivalent of a brand new pair of white sneakers. Instead, I started making sure that stuff had been "lived in" for a while in the woodshed before tossing them out live, or at least at "shows". However, jams are informal and relaxed, and not a bad call for educational approaches. I'm not saying toss taste out the window, but try some stuff. You're gonna throw out some clams, but so what. Same as with bluegrass, I'm not a jazz lifer. But I did play jazz standards for many years. Got started with "casuals" at society gigs. These often contained a "dinner set" and I'd try stuff as I was reading charts out of the Real Book. Nobody was really listening anyway, they were eating and socializing. Perfect opportunity for some trial & error education. But when hired for quartet work at restaurants and such where jazz was the featured program, it was back to "go for what you know", with the superimposed concepts and lines back to being relegated to the woodshed.
I'm not a big hot dog with showboat licks on banjo, largely because I've logged in less time with that instrument. Mandolin is interesting; I've gigged it for 5-6 years pretty regularly now. Can't zip around on it the same as on an instrument I've been playing for over 40 years (guitar), but the tuning in 5ths does seem to allow for some facility, particularly with mando-friendly keys such as D and A. Still learning, always will be I guess.
I'm running out of time and need to get to the teaching studio. I'll have to let the spell check thing go, hopefully it's not too bad. Y'all have a great weekend.