Ralph's Exercises for the Twanger PraxAx

General Principles
The groove rules. Steady solid rhythm makes music live and breath and move. You can get cute & fancy if you want to, but to hold a groove you need to be solid. This comes from practicing the basics till they become automatic and part of everything else you do. Keep it simple. Make the foundation strong.
Time
Use a metronome or recording to assure a good steady time line. Click track alone is fine. Keep it simple. Don t be in a hurry to get fast. It's more important to be smooth, steady, solid and comfortable. When you are relaxed and focused you can more easily move on to more complex patterns and make them work.
Touch
Listen to the shape of the notes you make. Listen to the attack, the sustain, the volume, the distortion, the overtones, the subtle differences between consecutive repetitions of the same note. Learn to make the notes sound the same. This is touch. When you can hear and control these subtleties, you will be able to move on to making interesting variations.
Speed, Endurance, Strength
Speed in itself is useless and boring. But speed lets you get to the next note when you want to, and gives you time to shape it to fit the groove. Speed means your fingers can move smoothly and that they will be responsive to your musical thoughts . Speed, endurance, and strength are tools to help you play better .
Consistency
Trying to sustain a repetitive pattern over a period of a minute or two may seem useless & boring . But if you are able to do it (it's not easy!) then you have the foundation upon which to build musical expression. The more precise and consistent it is, the more solid the foundation.
Goals and Patience
Identify and focus on simple particular parts of the whole. Set realistic goals and work toward them one at a time. Build your foundation stone by stone and make it solid. If it doesn't work today, just keep at it a while. When the muse senses anger or frustration she'll leave you. Sometimes you need to stay at a certain level till things sink in. Relax and have fun at it. Make the muse happy and she'll be your friend. Then one day, maybe after a good night's sleep, a whole new phase begins. Just keep playing

Fingering Styles  for the Picking hand
There are many different styles, rhythms and techniques for each instrument.
Some players use a combination of styles or change style or technique for different types of music.
Strum - up down movement across several strings, usually hitting the strings with the nail
Flat Pick or plectrum - used for strumming or picking - louder, easier on the flesh, different sound
- often used for faster playing styles like bluegrass or metal
Finger style - there are many variations, but these use a combination of thumb and fingers, or flatpick and fingers. Used by skilled players on many different instruments in many kinds of music incl rock, blues, bluegrass, classical, jazz, flamenco .
Fingering Styles  for the Picking hand

Exercise Patterns on one string only
Same note over and over. Up-down, alternating or down-down or up-up. Work for consistency, touch, time, speed. Try different fingers, different strings, flatpick, etc
First try to make the notes sound as nearly identical as you can and with indentical interval. Then try making them sound short or long, loud or soft and vary the intervals.
When you are comfortable doing a pattern on one string, try moving around to other strings during the pattern
for example, move to the next string every (1,2,3,4,8,12) notes
and/or Emphasize or soften every (2^nd, 3^rd, 4^th) note
and/or Skip every (2^nd, 3^rd, 4^th) note
You get the idea ? You can make up exercises to match your needs and musical interests

Two string patterns - use your imagination to extend this to 3 or more strings
1-2-1 2-1-2 1-1-2 2-2-1 repeated over and over with neighbor strings
Start on a different string every (2^nd, 3^rd, 4^th) phrase
Mix & Match different patterns for variety and complexity
Use strings that are not neighbors
Use different fingering styles
Vary the note intervals, durations, and emphasis

More Ideas
Same exercises as above, but notes may span more or less than one beat each
Q/q= quarter note (one beat) E/e= eighth note (2 per beat) S/s= sixteenth note (4 per beat)
Each note with same shape and intensity eg  (q q ee ee) (q ee q ee) (q q ee q) (ee q ee q)
Now place more emphasis on some notes in the pattern.
eg  (Q q ee ee) (q Q ee ee) (Q q Ee q) (q Q ee Q)
Copy patterns you hear on recordings, or read in books or on sheet music, or programmed patterns on drum boxes . These patterns sometimes have names like shuffle, rock, latin, reggae, blues, country, swing, jazz, techno,etc. Don't get fooled by the names. It isn't simple. There are infinite variations on even the easiest pattern. Build a strong foundation with exercises that develop time, touch, speed, accuracy, endurance.  When it comes time to find a groove, whatever name someone gives it, you'll have a better chance of making it happen.