The first item you need to be comfortable with is the grip.  This is your first point of contact with the rifle and needs to be fit to your hand.  A smaller grip is always easier to use than a grip that is far too large. 
The first grip we are going to look at is the basic M-16 grip.  Available with a finger notch and without this grip falls into the small category.  The grip works well with gloved hands but most competitors find the lack of gap filler unacceptable.

The Magpul MIAD series of grips is my personal favorite.  The ability to adjust the back straps is very convenient. I prefer the Medium back strap with the flat front strap.  The gap filler on the back strap places my index/trigger finger on the same plane as the pull on the trigger.  The ability to store items inside the grip is also and added bonus but is most helpful for keeping dirt and debris clear from the internals.

Magpul MIAD Grip

The Tango Down grip is considered to be a small grip.  US Palm, in association with Tango Down makes an improved version that fits larger hands and includes the back strap filler.  The upper portion is very thin allowing smaller hands to get a good hold of the weapon. The thicker lower portion allows the grip to be firmly grasped by the pinkie and ring fingers.

Other grips to include those by Ergo, and many other companies will meet the same needs the user desires.  With my experience the fore mentioned grips are my personal preference.

Magpul MIAD Grip on rifle.

Magpul MOE+

 A rubber coated version of the Magpul MOE grip. The MOE+ works really well.  Soft to the touch yet firm when gripped for use.