Hi Edward, just saw your message.  Kind of hard to explain with text, but here it goes using this track as an example:

https://www.youtube.com/watch?v=3B3g2sBmGGM

It's a standard 12 bar blues with a 4 bar intro, so it counts off the beats with a click at the beginning which goes 1...2...1.2.3.4., that gives you your tempo and 4 beats per bar, so think in your head 1.2.3.4.1.2.3.4 etc.

A way I like to write out these chord progressions is using the chord name and slashes to show the number of beats to play, so writing out 4 beats (one bar) of a G chord would look like this: 

G / / /

The chord name (G) represents the first beat and the slashes mean to play that chord for the remaining three beats.

So in this example, here's how I would write the whole thing out:

Intro (4 bars)

D / / / C / / / G / / / G / / /

Then into the repeating 12 bar form like so:

G / / / G / / / G / / / G / / /

C / / / C / / / G / / / G / / /

D / / / C / / / G / / / G / / / 

I guess I should put this up in the description of the video for others.  I think I put the chord changes in most of the other non blues songs I've posted.  Hope this helps!