I can't do a proper pushup

I do the kind of push up where you're on your knees and hands, instead of your toes and hands. Make sure to keep your back straight though, you don't want your booty in the air. I think I'm slowly working towards "real" push ups this way, I'd recommend it. I've also been following 30DS, which incorporates weights which I really like.

If your goal is fitness you absolutely need to strength train!

seconding nerdfitness! I've been having a little trouble keeping proper form with push ups as well and found this handy link. http://www.nerdfitness.com/blog/2011/02/15/proper-push-up/

Also I find that starting with your hands curled into fists instead of spreading your fingers can help you keep a little more stable. good luck!

Another vote for nerdfitness.com. I started using the beginner program a little over a year ago but couldn't do one proper pushup. I can now do 10 (although 9 & 10 are still a bit of a struggle) and my upper body strength has increased dramatically. I've also read that elevated or wall pushups are a good way to start; just make sure you are challenging your muscles.

Start with a wall or countertop pushup. As you get stronger keep lowering your hands until you are down on the floor. It will be better for you in the long run compared to going to your knees.

I agree with the wall or countertop pushup - that is what I am doing now. I am down from the kitchen counter to the bathroom counter - progress! I plan to keep going lower and lower. My knees aren't great so knee push ups don't sound fun, but countertop are great because you can do them when you are waiting for something to cook, or at work if you have a place to do it. Bathroom counter push ups you can do while you are rinsing with mouthwash for a minute too - so multitasking!

I know the feeling - i still struggle with push ups, and i do a lot of strength training.
You need to not only build your arms but your BACK and your CORE.
Planks and mountain climbers are perfect for core, try doing tabata (20 seconds on, 10 seconds off. There are lots of free apps).
You can also do halves; lie on the floor and push yourself up into push up position. From this i then SLOWLY lower myself back to the ground.
I also incorporate squat thrusts/burpees and pike press into my training, which works your arms and shoulders.
Bent over rows will help build your back up (just use something heavy, you could even use a child if you have one and make it a game).
You could also try man makers and inch worms.

There are so many body weight activities you can use to build muscle without heavy weights but eventually you will need to use them.

There's actually a ton of good advice here already, so I'll summarize a bit too.

Since I'm in the military we have to do pushups. You get better by doing more pushups! If you can't do one yet, get started in these ways:
* Angled Pushups - Start at a countertop, then a chair, and slowly get lower to the ground until you can do a full pushup!
* Knee Pushups - These are best when you've tired yourself out on regular or angled pushups.
* Pushup but rest on the ground - This sounds crazy, but when we were in basic training and put on our face (doing pushups) but too exhausted, our drill instructor had us keep going by doing this. Slowly lower yourself to the ground from a full pushup position (hands and toes), then keeping your whole body straight like in a plank, push all the way back up from the ground. The key is keep that core tight. Don't let your upper body come off the floor first. It all goes up at once!
* Planks!

Form matters most! Everyone and their mothers have videos of pushup form including nerdfitness and even medical sites! Basically you should be in a perfect plank throughout the entire pushup. No bobbing of the head, no movement in the hips. Watch some videos and do them in front of a mirror as much as possible to make sure you're doing them right. An incorrect pushups can cause all kinds of issues, especially in your shoulder/neck/spine if done incorrectly.

I actually love planks and bridges because I have back problems, and back pain is more likely to fail me on a pushup than my arm strength. As far as building up, find a program you like and stick with it. Others seem to like nerdfitness, which I'd never heard of but will take a look. I liked the 100 pushups program. Even though I never progressed through all the weeks up to 100, I saw a significant improvement in 8 weeks. http://hundredpushups.com/

Another easy one we do in the military all the time is alternate days. One day, give yourself a goal like 100 pushups and 100 tricep dips. Don't freak out! You have all day to do this, and do them 5 or 10 at a time. The next day do some legs and abs. We like squats, pushups, and situps because we can do them right there next to our desk.

Edit: Also, there are different kinds of pushups. In the military, more women do wider pushups with their elbows going farther away from the body, which works the chest more. The men prefer tricep pushups with the arms very close to the body.

I've been doing body weight exercises for about 2 months now and it's been great. I got the book "You are your own gym" and love it. It has exercises from easy to very difficult.