I don't know about you, but my time is valuable. I don't have the luxury of experimenting with strength exercises that might work, might be safe, from celebrity trainers who might know what the hell they are doing! All the big forums are filled with 'experts' who repackage old knowledge and then act like they just invented the wheel. You have to sift through the BS and find drills that make sense and build strength... for you.

I use four criteria when selecting bodyweight strength exercises:

It has to be simple to learn. Not necessarily easy to master, mind you, but simple to acquire. If I can't get the basic technique down in 5 minutes, I'll pass. I'm looking for strength and strength-endurance. If I want to learn technique, I'll sign up for ballet.

It has to be safe to perform, repeatedly. Look, there are no guarantees you won't get injured bending over to tie your shoes. But what good is your time spent learning some fancy-ass killer commando move if you strain your hamstring, tweak your shoulder, and you ligaments and joints are throbbing. Is that fitness? Leave the one legged-on-your-toes bunny hop for the advanced class. Basic, fundamental moves you can do over and over is what builds strength and strength-endurance and keeps you injury-free.

It has to be balanced. I'm looking for some kind of balancing effect on the muscles when I work out. If you run on a treadmill, eventually you'll hurt you knees. Why? You're working primarily your quads and calves, very little to no hamstrings and glutes. Do one kind of pullup only, you'll probably create some shoulder problems over a period of time. Mix your grips and you'll stay injury-free. The drills I recommend work muscles  balanced fashion (usually) keeping things simple (see point #1) and keeping you injury-free (point #2)

You should feel better after a good strength session, not worse.

Ok, on to the No-Time Power Leg Drill. This is NOT original. ( What is?) Jason Ross of www.trainoutpain.blogspot.com was kind enough to clue me in on this terrific leg drill. (Jason is one of the few experts who earns that title every day, and a gentleman to boot. I urge you to visit his excellent site for more info).

Get into a lunge position. Back knee is on the ground. Back is straight and vertical. Don't lean forward! Front thigh is parallel to the ground, shin is vertical.

With your hands down by your hips, make two tight fists, squeeze, and also make sure to squeeze your butt cheeks tight. Now stand up hard.

When you return to the ground don't just drop, but pull yourself down. Obviously decelerate so you don't bang your rear knee.

Do five repetitions with each leg, then switch.

Find it too easy? Do the same thing but place your rear foot so that your rear instep is against the floor, not the ball of your foot. Not so easy anymore.

You can also do this with a weight vest on. I prefer not to do this with dumbbells in my hands,  I think the balance required with weights throws off the form a bit.

This is a simple, proven drill that will strengthen your legs noticeably, immediately. You avoid balance issues and a steep learning curve, and almost anyone should be able to do these with just a little perseverance. Give this power drill a try. You'll have iron legs in no time.