The best warm up exercises for fingerstyle guitar are guitar scales. Here are some scales that you can use to warm up before playing.
How to Warm Up with Fingerstyle Guitar Scales
When practicing guitar scales as a warm up, be sure to play the scale slowly and place great emphasis on finger placement and accuracy. The goal isn't speed. The intention is to get used to co-ordinating both your fretting hand and your plucking hand.
Instead of thinking of practicing scales like a chore, use them as an opportunity to improve finger accuracy and tone.
Which Guitar Scales can we use to warm up?
You can practice both the major scale and the minor scale to warm up. But in this article I will propose some other scales that you can use with easier or more comfortable fingering patterns.
The C Major Scale for Fingerstyle Guitar
Let's start our warm up with the major scale - the C Major scale over two octaves. This is playing the notes C to C without any alterations (sharps or flats).

Normally, when you pluck repeated notes, you'll want to avoid using the same finger twice in a row. I teach a method that I call walking fingers, where you alternate plucking the same string with the index and middle fingers.
Using Three Fingers Per String
Since we have grouped together three notes per string, let's instead of using only two plucking fingers, use a combination of three separate fingers. Use either the thumb, index and middle fingers or the index, middle and ring fingers of the plucking hands in repetition as you play the scale.
The Problem With The C Major Scale Fingering Pattern
The problem with the three-note-per-string fingering pattern is the wide stretches between notes. The C Major Scale is a little better in this regard because it's in a higher position, so the distances between frets is less large.
The Ultimate Guitar Warm Up Scale - G Major
Once you have warmed up with the C Major Scale, it's time to increase the finger stretches. You can also work on increasing the speed.
Let's continue our warm up routine with the G Major scale. This scale consists of the notes G, A, B, C, D, E and F♯. Play the scale ascending and descending, with the following fingering pattern:

The Chromatic Scale
The chromatic scale is what we get when playing all the notes on the guitar that are between the octave. We noticed with the major scale that there are "gaps" in the scale notes, caused by the unequal distance between the notes. The chromatic scale has no gaps.
The chromatic scale on the guitar contains four notes per string. To perform the chromatic scale on the guitar, start at any note on the sixth string. Play each fretted note with each of the fingers, then switch to the following string, shifting the hand downwards by one position.

The Harmonic Minor Scale
The two octave minor scale is not very much fun to play on the guitar because it involves extensive position shifts and not very logical fingering patterns.

Locate the tonic note, then play the supertonic a whole step (two frets) above the tonic, and the mediant a half step above the supertonic. Next play the notes using the same fret distances as the previous string.
To play the last two notes of the scale, shift your hand over one fret from the starting point and play the leading note, followed by the tonic a half step above the leading note.
The Freygish or Phrygian Dominant Scale

A mode of the harmonic minor scale, the Freygish scale or phrygian dominant scale, is lots of fun to add to your warm up routine because of its exotic sound.
The Whole Tone Scale
This scale has a tone or a whole step between each note in the scale. The distance of a tone on the guitar is two frets. There are six notes total to this scale.

It's very simple to play the whole tone scale over three octaves. Unfortunately owing to the fact that there are two frets between every note on the scale, the stretches can be quite large. So this scale maybe isn’t a good choice for warming up the fingers.
Pentatonic Scales
The minor pentatonic scale which contains five notes and is simpler to play than the major scale. The pentatonic "box pattern" is very straightforward to play on the guitar. It's also a classic scale used in guitar solos found in Rock music.

I love the sound of the pentatonic scale. Unfortunately, once you get past a certain point in your guitar playing, practicing the pentatonic scale gets a little boring
The Hirajoshi Scale
The Hirajōshi scale, or hira-choshi (Japanese: 平調子) is a type of pentatonic scale that is excellent for working on position changes in your warm up. Play this scale slowly and be very precise with how you place your fingers.

The Double Harmonic Major Scale
This scale contains a lot of semi-tones, which means there are not many finger stretches.

What to Play After Warming Up
If you are still looking for more fingerstyle guitar exercises, there are lots of songs you can play in the course Play Fingerstyle Guitar Now!