#1
Ive been trying to improve the area of my playing that revolves around playing lead parts and chords together; think of Little Wing and Under the Bridge. Ive become comfortable playing chords with my thumb which allows the use of all four fingers, which is apparently important. But I seek to know which scale notes I should use along with the chords. For example: Im playing an Am progression and I want to hit a F and then immediately play a lead. Is it more common to play notes of the F major scale or in the Am scale (key of song)? I realize that for a long lead or solo I would play an Am lead most of the time, but Im talking about a couple notes here and there between chords. Thanks for any help.
#2
Am, since that is the key and tonal center. F major has Bb, which will sound kind of dissonant when playing in a minor, it probably wouldn't be too bad, since over Am, that will sound like phrygian, but stick with Am/
#3
start out easy, play into the notes of the chord with just one note in front of every one (you can still play it on several strings simultaniously) the notes you use are derived frm the scale of the chord, so in a basic minor chord, you might hammer in to the 5th from the (perfect) 4th, and into the 8th from the b7.
you can also start on the chord tone and lead this back to another one (or the same depending on where your line's going) through a scale note, so again in a basic minor chord you might want to play the chod, and pulloff the high 3rd to the 9 below it (2nd note of the scale) here's an example of this basic chord melody apprach:


Bm
|--------2-------------|---
|-2---2-2-3p2-2--------|---
|-2-4-4-2-----4p2------|-4
|-2-4-4-----------2h4--|-4
|-2--------------------|-2
|----------------------|---


now, you're gonna want to actually change this into a bit of a melody, so you want to use more notes, these are derived from the scales you'd normally play over that chord, start out with just playing a line but on the accented chordtoned, play the whole chord (probably also the first note of the meassure so you start with a chord)

an example would be (it's quite jazzy in 5/4 but all B minor7 chords)

(swung 8ths)
in B natural minor : 
     |--3--|  |--3--|   |---3--|  |--3--|        
     E  E  E  E  E  E   E  E   E  E  E  E  Q     
E||---------------------------------------------|
B||--3--2--3-----------10--8--10-----------7----|
G||--2--------4-----6---7---------9-----7--4----|
D||--4-----------5------9------------------7----|
A||--2------------------9------------------5----|
E||---------------------------------------------|


        |--3--|         |--3--|              |---3---|                     
  E  E  E  E  E  E  E   E  E  E   E.   S     E   E   E   W                 
-----------------------------------------|--------------------------------|
--7-----7--------7--8--10--7--8--12---12-|--14--12--10--12----------------|
--7--------7--6--7---------------11------|--11----------11----------------|
--7--9-----------7---------------12------|--12----------12----------------|
---------------------------------12------|--------------12----------------|
--7--------------7-----------------------|--------------------------------|

or in dorian : 


  |--3--|  |--3--|   |---3--|  |--3--|        
  E  E  E  E  E  E   E  E   E  E  E  E  Q     
---------------------------------------------|
--3--2--3-----------10--9--10-----------7----|
--2--------4-----6---7---------9-----7--4----|
--4-----------6------9------------------7----|
--2------------------9------------------5----|
---------------------------------------------|


        |--3--|         |--3--|              |---3---|                      
  E  E  E  E  E  E  E   E  E  E   E.   S     E   E   E   W                  
-----------------------------------------|--------------------------------|
--7-----7--------7--9--10--7--9--12---12-|--14--12--10--12----------------|
--7--------7--6--7---------------11------|--11----------11----------------|
--7--9-----------7---------------12------|--12----------12----------------|
---------------------------------12------|--------------12----------------|
--7--------------7-----------------------|--------------------------------|


if you can't follow up with the chords, play them all as a simple powerchord in the same position at first.

if you don't like jazz, here's a way i like to roll around your chords


(again in b minor, swung 8ths)
     |--3--|                              |---3--|   
     E  E  E  E  E  E   E     E  E  E  E  E  E   E  
E||--5---------------------|------------------------|
B||--7--7--------9---------|--7---------------------|
G||--7-----9--7--6---------|--7--x--------7---------|
D||--7--------------7--11--|--9--x--7-----9--7------|
A||------------------------|-----------7--9-----11--|
E||------------------------|------------------------|

   |--3--|  |---3--|                          
   E  E  E  E  E   E  E  E     H.          
----------------------------|--7------------|
---9--7-----7---------------|--7------------|
---------9--7--9--11--7-----|--7------------|
--11--9--7--7---------9-----|--7------------|
---9------------------9--9--|---------------|
---7------------------7-----|--7------------|

it's in 3/4 if you weren't following, the end can be pretty tricky so you can leave the higher or the lower notes out, the B minor chord is tackled with a dorian scale all the way through, try playing this but use a harmonic minor scale instead

just mess around with this as much as you can, you'll end up sounding like 2 guitars while playing just one
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#4
Someone might have said this already, but if I were you, I would use F lydian.

The key of A minor is the same as C major, obviously. The relative mode of C major whose root is F is F lydian.