need left hand technique tips

My left hand mutes the A string when I'm trying to reach the G string. The skin where the pointer finger meets the palm overlaps when I am extending my fingers on an Am chord for example.

Keep the flat of your thumb positioned roughly in the center of the back of the neck. It can come closer to you, but should stay roughly centered so that when you press the strings you are sort of pinching your fingers against your thumb with the neck in between. Do this instead of wrapping your thumb around the top of the neck or resting the neck in the space between thumb and forefinger. That should give you bunches of space between the neck and that area you are having trouble with.

Yes, what Teek said, put your left thumb in the middle of the neck. Think of your fingers as arches, and only let the tips touch the strings (unless you are doing a barre chord). Trim your fingernails short on your left hand so they don't get in the way. Get a strap if you are having trouble holding the neck up while playing. Think of your fingers like a tarantula's legs walking on your fretboard. You will get better with practice. If you hear a dead string, look carefully at the cause, and adjust your position.

Welcome to UU.

–Lori

Great points from above as moving the thumb will move the bottom of your hand away from the uke. As you get better, start turning the uke to be more vertical than at the angle. Instead of looking at the fingerboard, you should rely on the side dots as guidance to where you are. This will help you get your hand in the right position and allow you to play cleaner notes and bar chords will become easier.

Erich Andreas (yourukesage.com) says he puts a dot in the center of the tips of his new students' fretting fingers with a Sharpie. Then he teaches them to fret with just that dot. You may not need the dot, but it's a great learning tool with or without the marker. If you always strive to fret only using that dot (real or imaginary) you will naturally bring your wrist forward and point your fingers at the frets rather than at the ceiling. This is what you need to do to fret effectively. It's been my experience that the thumb just follows good hand position. The hand position and finger technique are vital. The thumb will work itself out.