Here are my first thoughts, and some hints...

Music is like speech, with words, phrases, sentences, paragraphs.

Remember the phrase you just played, and develop it (cut out the waffle).

Don't practise scales only in one way - find a few different ways to practice each scale.

Learn to play each scale firstly in one position, then just on one string.

Play a whole tune on one string only.

Sing what you play, play what you hear.

Learn simple tunes - 'Happy Birthday', 'Oh Susannah', 'Stars and Stripes' etc

If you are sustaining a wrong note, move it up or down a semi-tone: it will then fit.

Don't play too many notes: more is less.

Don't fill all the space: listen to what is going on around you.

Use backing CD's.

Develop your sense of relative pitch: learn to sing intervals: a fifth, third, seventh, flat fifth, second etc.

Aspects of improvisation
So what does learning improvisation entail? The following subject areas are the things I think about when I teach improvisation:

Melody

Melodic devices

Rhythm

Harmony

Timbre

Phrasing

About backing tracks
It is very important to practice improvising with an accompaniement. You will not have an obliging friend continually on hand, so it means getting some kind of electronic backing. In the old days that meant taping some chords then playing along to your tape. Then came playalong LP's and then playalong CD's (get some of the excellent CD's in the Jamey Aebersold collection). But then came

Band in the Box

This is an amazing piece of software that allows you to type in the chords you are working with, plus a style (eg 'jazz waltz', or 'samba') plus an instrumentation (eg bass, drums and guitar trio, or, say, piano only), plus a tempo, and playalong. You can loop a section you want to concentrate on if you like. If you are a jazz player, get this software now! It will help you improve timing, ear-training, harmony knowledge, repertoire-building and much more. You can get it from Jazzwise at www.jazzwise.com