What are your favorite warm-up exercises and why?

I used to do scales, but now I just dive right into the pieces that I am trying to learn. I get enough of a workout with those pieces. Plus, after doing lots of technical exercises, I have found that the pieces that I like to play often do not have 1:1 mappings to the standard exercises.

What I really should be doing is creating little micro-exercises out of the repertoire.

Martin, you mentioned that Villa-Lobos' Prelude No. 1 is going to be the next piece for our study group. I am not sure how serious you are about this ... but I would be happy to hear about any exercises to do to help you play VL 1.

Edit: I just saw the announcement for the VL 1 study group.

Martin,

You have a very good question.

I think I probably tried every warm up that exists.  And I do believe they worked.  

Now I only do right hand and left hand techniques for about 15 minutes, then I go right into a piece.  When I see that I have difficulty in an area of the piece, I'll focus on it and go over it up until I get it down.  

I do try to get the tone down as close to what I think it should be.  I am not an expert but I can hear it when it doesn't sound good.  And to double check, I record myself to hear how it sounds and to see the dynamics of each note, what is the spacing between each note.  

This has been working for me.   

If we are talking about 'Warmup' and not exercises, I usually devote, with a timer, 10 minutes to get my fingers and mind thinking about music. I usually pick a scale for the day, set the metronome at a relaxed tempo, i.e., 60, and simply improvise, going through 3rds, 6ths, etc, and playing whatever comes to my head.  I concentrate on triplets, 16th note bursts, quintuplets, 8th notes, slurs, hammer-ons, and position playing up and down the neck. I also mix it up with apayando, and triando, but always with good tone production. During this time, I am also constantly adjusting my nails to get the best tone I can get, filing, and smoothing the nails with 2000-grit wet/dry paper till I'm happy. Then I jump into the real music.  I spend no more than 10 minutes doing this, and I find my fingers on both left and right are sufficiently warm and ready to go after this.       

At one time, my practice/warmup/skill development routine consisted of scales, arpeggios, slurs, finger independence, and barre exercises. Now I do less and do it at a slow pace.  What I find enjoyable and productive is to work on a piece of music by breaking it down into the difficult and challenging segments, working through these segments slowly, preparing/planting, sometimes focusing on fingering transitions without regard for the rhythmic notation until my fingers are ready to respond to the music as notated. Eventually, I gain the ability to play the piece from start to finish.

In the past I'd go through a very detailed list of technical stuff like slurs, chromatics with different left hand and right hand combinations, arpeggios, etc.
Nowadays my warm up is rather minimalist: I'd work on my attack and tone using open strings with different right hand combinations and tirando/apoyando (free/rest stroke), whilst adjusting my nails to get a nice sound for the day. After that I like to warm up my left hand fingers doing a chromatic scale with a lot of vibrato at different speeds (very slow, normal, fast).

I keep it rather short, like 10 - 15 min total.

Guiliani arpeggio studies Groups 1, 2, 5, 8. Then some selection of Segovia scales. Then Sor Study #1 in C and the Sarabande from the Bach Bm violin partita. Takes 1/2 hr. All ready to go after that.

I have just revised my warm up / exercise routine after watching Martin's Livestream.

1. Slur studies (Th. Vilateau TB lesson). Right now I am just doing 2 finger slurs.

2. Stretches that Martin demonstrated in his Livestream (note: 3-4 is a killer!)

3. Chromatic scales based on Inestal's TB lesson. I set the metronome at 50 and do I/m free stroke, I/m rest stroke, a/m free stroke. I increase the rhythm each sequence as 2,3,4 notes per beat. I continue with I/m (free and rest) 5,6 and 8 notes per beat.

4. VL etude #1 - I start w/ a/m only on just an 'e' minor chord - 2,3 and 4 notes per beat. I then play the first section of the etude w/o repeats using all fingers (sans pinky) at 3,4,5,6 and 8 notes per beat. (I find quintuplets really challenging to maintain.)

5. Cross string trills using the same system as before.

I can usually do this in 30' - 45' which is about all I put up with.

My first classical/flamenco teacher, Ron Radford, showed me a chromatic scale exercise he learned from his early mentor, Carlos Montoya. If anyone is interested I'll attach it to a post. It ascends/descends twice with different fingerings. I play the first half with free strokes, the 2nd with rest strokes. I play it with i and m, then m and a, then i and a. With the metronome at 100 - 112 I play it in 8ths, 8th-note triplets, and then sixteenths. I often don't do the m, a, run in 16ths but I do p and i. After that I'll do one of the arpeggio etudes, Brouwer 6, Villa Lobos 1 or a Giulliani opus 48 #5. I usually do a few passes on the etude with the metronome, gradually increasing tempo. If I'm doing the Villa Lobos I only play until the first couple of diminished 7 chords.  I finish with the slur exercises in Pumping Nylon.