Originally Posted by: MickyDsHow do you transcribe from one key to another on guitar?[/quote]
The term you are looking for there is transpose.

Transposing on the guitar is usually very easy because it simply means to move the pattern of chord or scales up or down the neck. Keep the same exact shape, just move it X number of frets.

When we learned barre chords in GF2 this is exactly what we are doing: transposing to get different chords with the same shape.

http://www.guitartricks.com/tutorial.php?input=450

Originally Posted by: MickyDs
So if I am playing a Amaj blues how would I know what to play in Cmaj?

The same exact shapes, but 3 frets higher, because that is the distance on the guitar from A to C.

Here's a blues riff in A major. Looks familiar, yes?

|-------------------------------------------|
|-------------------------------------------|
|-------------------------------------------|
|--2-2-4-4-5-5-4-4--------------------------|
|--0-0-0-0-0-0-0-0--------------------------|
|-------------------------------------------|

To transpose this riff to C major simply move the whole pattern, intact, up 3 frets so your root note is on C instead of A.

|-------------------------------------------|
|-------------------------------------------|
|-------------------------------------------|
|--5-5-7-7-8-8-7-7--------------------------|
|--3-3-3-3-3-3-3-3--------------------------|
|-------------------------------------------|

Make sense?

Next, suppose you are playing blues licks using the A major pentatonic box. Notice that the 1's, the scale root notes, are on A notes.

E ||---|-6-|---|---|-1-|---|---|---|---|
B ||---|-3-|---|---|-5-|---|---|---|---|
G ||---|-1-|---|-2-|---|---|---|---|---|
D ||---|-5-|---|-6-|---|---|---|---|---|
A ||---|-2-|---|-3-|---|---|---|---|---|
E ||---|-6-|---|---|-1-|---|---|---|---|

To transpose this to C major, we simply move the whole pattern, intact, up three frets so that our 1's, scale root notes, are now on Cs.

E ||---|---|---|---|-6-|---|---|-1-|---|---|---|---|
B ||---|---|---|---|-3-|---|---|-5-|---|---|---|---|
G ||---|---|---|---|-1-|---|-2-|---|---|---|---|---|
D ||---|---|---|---|-5-|---|-6-|---|---|---|---|---|
A ||---|---|---|---|-2-|---|-3-|---|---|---|---|---|
E ||---|---|---|---|-6-|---|---|-1-|---|---|---|---|

Make sense?

In this tutorial I play a wide variety of different blues riffs & licks. Lessons 2 & 3 are in A, lesson 8 & 9 are in C.

http://www.guitartricks.com/tutorial.php?input=1108
[QUOTE=MickyDs]Also what scale could I use to jam with? Is it F# blues or could I use a A blues as well while in the key of A maj?

I think what you are looking for here is that you can use either pentatonic major or pentatonic minor to play blues licks. There are lots of options, so it does get confusing.

I show the same group of notes using A minor pentatonic in this tutorial.

http://www.guitartricks.com/tutorial.php?input=1614

And they can also be used to play in C major pentatonic here!

http://www.guitartricks.com/tutorial.php?input=1646

This tutorial also shows how to incorporate both pentatonic major & minor to use in solo licks.

http://www.guitartricks.com/tutorial.php?input=1441

Have you gone through the Blues Course? Anders does a great job of explaining soloing ideas in those courses!

Also, in the above tutorial I show a bunch of different approaches to blues licks. In these tutorials I show you the basic ideas that most blues licks are based on. They are all in A, but are all transposable to C by moving them up 3 frets! :)

http://www.guitartricks.com/tutorial.php?input=217
http://www.guitartricks.com/tutorial.php?input=232
http://www.guitartricks.com/tutorial.php?input=826
http://www.guitartricks.com/tutorial.php?input=244

Ask more if necessary. Have fun!