Check out the website below. Sign up for the news letter and get the free beginners guide to a handstand. It helped me A LOT and is also full of good advice about holding a hand stand.
http://www.lostartofhandbalancing.com/I have a few quick tips for you both though, some of these tips are for holding a gymnastics style handstand (which is what I do personally and I think they look a lot better

).
Some terms:
Over-balance: Falling toward your back
Under-balance: Falling toward your chest
Hand placement: Your pointer fingers should be pointing towards your back and should be parallel to one another.
The most important aspect of a hand stand is the kick up!
I have a solid kick up can hit my sweet spot 9 out of 10 times, but I still practice my kick
everyday. Its what I use as a warm up to my daily workouts. By practice I mean I kick up
hold the hand stand for 5 seconds come down and kick up again over and over.
If you are kicking up against a wall, kick up slowly. If you kick up to softly you will just land back on your feet. Just increase the force at which you kick up until your feet gently make contact with the wall.
General tips:
Keep your arms straight and elbows locked out. Your shoulders should be engaged, basically you want to try and touch your shoulders to your ears.
Look towards a spot between your hands, look mostly with your eyes and move your head as little as possible. This will help you keep your back as up right as possible and take some of the arch out.
All of your balance should be coming from your fingers and wrists. If you overbalance press into the floor with your fingers. When in a handstand you should try to be in a constant state of overbalance, using your fingers and wrists to keep you from falling over.
You should be keeping your body, from your shoulders to your toes, as tight and stiff as possible (it helps if you point your toes). I try to think of my entire body as a solid board so when I press with my hands my entire body shifts, thus only small movements are needed to change your center of balance.
Ok, so when you kick up against the wall (that is your back is facing the wall) there are a bunch of different things you can do. But first when you kick up try and place your hands about a foot from the wall. Once up there you can lightly tap your feet off the wall and try to keep yourself from falling back into the wall.
A good exercise to get the feel of what a straight hand stand feels like is to put your finger tips about 1-2 inches from the wall and then kick up and try to get your hind end and your heels to make contact with the wall at the same time.
There are lots of exercises that you can do when against the wall but they are hard (except the push up) to describe in writing, if enough people bug me I could make a few videos.
Now for the handstand away form the wall.
You should ALWAYS start with just holding a static handstand, even if your goal is to walk on your hands.
When you kick up do not walk around AT ALL. Walking around to stay in the hand stand is not hand-balancing you are simply stepping in the direction at which your body falls. This will lead to bad habits that will be hard to break.
So, kick up into the handstand and do everything in your power to stay upright without moving your hands. Right at the last moment either roll or cartwheel out of the handstand.
And remember that the kick up is the most important part, if you dont have a consistent kick up it will be very difficult to hold a handstand with any consistency.
Ok, I have to go if you have any questions just ask away!
Good luck and Practice EVERY DAY!