I'm Dave and I'm an alcoholic.........Ooooh, wrong room!

I did a forum search for what I'm about
to ask and it didn't turn up anything I could understand
that would help me out. So I'm going to ask again in a
different way than the other topic and see if it helps.

Is there a simple formula or even a complicated one that
can be answered in a forum format that would help me figure
out for myself what common modulations can be made in a
given key?

I'm probably wrong in thinking that there are
limits as to what key changes can be made. Can you change
to any key you like as long as you can make a good transition
into the new key and make it sound good? And is there
a formula for the turnaround?

My ear is not trained well enough to just listen to a
say a blues tune and hear and know the changes in key.

And by the way is building, playing and singing major
and minor thirds the best way to train your ear or is
there another way?

I really didn't set out to ask so many question at once
but it seems like one just leads to another.

I'm used to just reading and playing standard music notation
and when you read music you don't have to really learn anything
about key changes because you just play the notes on the
page. Also I played trumpet so I didn't even have to learn
anything about chords and chord changes when reading music.
Just one note at a time. But sense picking up the Guitar
I have learned a lot about chords, building and what not.

I know that I can get tab and learn about any tune I want
but I'm not learning seems to me the things that will make
me what I want to be with the Guitar.

Thanks in advance!
There are common modulations, for instance modulations to the dominant, sub-dominant, relative minor and direct minor (I think the guys here call it parallel minor) are all very common and the change is quite easy on the ear.

Let's let at an example: If you were in C Major you could modulate to F Major, G Major, A minor or C minor. These are common modulations, but as you said, you can modulate to any key you think sounds good.

And building, playing and singing is definitely a good way to train your ear, also record some thirds and play them back at random and see if you can identify them.
"Battle not with monsters, lest ye become a monster, and if you gaze into the abyss, your eyes will get sore after a while."
A common way to lead into a new key is with a pivot chord. Basically you use a chord that is found in both keys to change into the next key. A lot of the time the pivot chord is the dominant of the new key, but it sounds better as a dominant 7th.

I'm sure there are more ways, that's all I know.
"Battle not with monsters, lest ye become a monster, and if you gaze into the abyss, your eyes will get sore after a while."
The easiest and therefore most common modulations are those from the current key, to any chord in that key.
For Example in Cmaj..... You could modulate to Aminor, Dminor, Eminor, Fmajor or Gmajor.

These chords are closely related, one because they are in the same key...
And also if you look at it like this:

Cmaj Amin
Fmaj Dmin
Gmaj Emin

You see that it is the tonic, sub dominant, and the dominant chord... and all their relative minors..

When you modulate to one of these chords/keys... then you are only adding in a flat, or adding in a sharp....

Modulating to the sub dominant, is going flat.
and to the dominant is going sharp.

To be honest, im not really a big blues fan, so i dont know much about turnarounds....
And as far as ear training goes, I use a site called www.good-ear.com

Hope that helps....