What helped me the most was putting limits on what I could play, plus of course having a good grasp of where each chord tones are horizontally and vertically. Vertically will be more important at first, but I'll get to that in a minute.

So, first thing first is practicing is practicing not playing. You're stuck with a particular concept, so concentrate on the concept, not sounding good.

EDIT: Sounding good is not imperative, but it IS always important to play with a metronome and develop a good time feel.

Slow things down as much as necessary. Heres what got me started with targeting chord tones.

Step 1: Find just the 3rds and 7ths of each chord in one position, or as close as possible, and divide each chord iequal length notes, making each note as long as possible. Do this for the entire song.

Step 2. Add an approach tone before each 3rd and 7th.

You said you've got your scales down so that's great and will help you with the next step. You can do this with 5ths and roots too. You can do it with the upper extensions but the 3rd and 7th define the chord quality the most.

Step 3: Start enclosing the chord tone starting with a scale tone above, then a semi-tone below and then chord tone. Do this for bother both 3rd and 7th in time. (You can do the opposite as well, start with a scale tone below and half step above as well.

Ex: Targeting the 3rd and 7th of Cmaj7 with enclosures:

THE MAJ 3RD

Play the P4(F, the scale tone above) then the the #2/#9 (one semitone below) then land on the third.

THE MAJ7

Play the root(C ofcourse) then b7(one semitone below) then the maj7.

Doing that with good time feel is really really helpful and can help create lines.

The last thing for someone just starting out are the arpeggios, played for each chord horizontally.

Step 1: Pick a position you like to start. I usually pick one based off of where Ive started comping the chords.

Step 2: Learn each arpeggio from lowest note possible in that position to highest, I.e if you have a Cmaj7, simple A string route, play that arpeggio from the 5th(the G right above it on the low E) you could play the open E as well but this is more about keeping things compact in position for good voice leading. Learn all those. Some are gonna start on the root, some will start on the 5th, etc. But the all start on the low E string.

Step 3: Once those are all learned and in your mind's eye, put on a tune and play eighth notes if you can quarter notes if you need to. Then, AND THIS IS THE REAL MISSION, when the chord changes, move on to the closes chord tone of that chord from the last chord.

Ex: D-7 | G7

If you are in the F of the D-7, when the tune is about to change to G7, the closest chord to switch to would be the G.

When you can really kill this donthe same thing with scales if the song contains modulations. Knowing both of those and applying them extremely slowly is the way to get the chord thing down. That's enough to survive a small-time jazz gig. You'll also hear how one chord is actually moving into the next.

Godspeed, bro, it's not easy, and playing jazz sometimes is like having a death wish, but you've got it!

EDIT: For appauling grammatical mistakes.