as the title implies I'm having trouble playing the G chord. I have been following this tutorial on youtube:which explains it pretty well, only problem I seem to be having is whenever I lay my fingers down my ring finger gradually starts to slip off of the E (6th string), or rings out a bit buzzy despite me holding down the string considerably. Could this problem possibly be due to finger strength? What do you suggest I do?
As in the comments.Your hand and fingers (and indeed arm) are not the same as everyone else's, so those fingers he's using may not be the best for you. A pinky on top E string may work better, or even both ring and pinky on 2nd and top strings respectively, for a slightly different sounding G chord. This works well for some, as those two fingers are stronger together.
You could also try ring on low E, middle on 5th and pinky on top string. The transition then to Em, which is common, will still work, but with a different fingering for the Em.
As David says, the arm position is important for G. Notice it's easier to produce more pressure on the fingertips by moving the elbow away from the body, using the bottom string as a fulcrum point.
What you need to do is use the guy's idea of common fingers for related chords, which is sound, but take it further. You may, for instance, find an alternative fingering for E to A which means another finger pattern for the A. In other words, don't just play any chord like it's shown in a lesson (specially on the net..!) but think about other options for the future.
The idea of a footrest: probably won't help much. but instead strap the guitar on so it's in a better position than on one leg, and high enough that your wrist isn't contorted. Play around with the angle of the neck, and please don't move the guitar so you can watch the fingerboard better. If it's that desperate, play in front of a mirror!
And try very hard not to strum those '6 open strings' at the end of bars to give yourself time to change like he does! It can sound pretty amateur. Simple solution - don't play the last upstrum - or - get the changes fast and tidy enough that you can do them properly.
There are two tricks by which you can compensate the lacking strength of your hand and fingers:
Instead of cramping the neck with the thumb right beyond the neck and pushing down the strings from above by your fingers - try to hold the wrist stiff, then turn the left arm by lifting the elbow slightly up turning outside left, as you were breaking the neck of a goose - but don't break the neck of the guitar! You are using the lever principle and the center of rotation is the point between thumb and the fingers. What happens: the strings are pressed on the frets without need of strength in the hand!
Now have a look at your right arm: Where is your elbow? It is hold above the body of the guitar touching the top of the soundboard. By pushing slightly with your right elbow of the guitar body and pressing the instrument softly against your body the neck will be pulled against your left hand and your fingers. Thus you may also compensate the missing strength of the left hand and fingers by using again the law of levers.