Many of this has already been said, but I'll post exactly what I did when training for the military. I couldn't even do 1 when I started in high school either.
- Start with weighted training. Curls, tris, bis, shoulders, back, and chest. ALL of it + ab work is needed for push ups. Planks, even from the knees, pull ups (When I say this I mean the sissy girly ones, where your legs are straight and on the ground and you're lifting your body weight up to a bar vs off the ground and perpendicular to the ground.), and modified push ups are VERY key. The key is to have good form for all of it. LOTS of youtube videos on the subject, and there's a training guide literally called 100 push ups challenge that goes from zero to hero. I was also doing cardio which I believe is key in having the endurance to continue to plow through push ups.
Nothing breeds a good push up like push ups.. so as much as you can do the other stuff (weight training, modified push ups on walls and then on your knees) as soon as you get to doing correct push ups on your own, forget the modified stuff with the exception of the knee push ups. Just do real push ups, then drop to your knees for the rest when you reach muscle failure.
Also, keep a diary. It can be hard to see progress without one. Nothing fancy, just a note saying how many you did that day before reaching muscle failure.
If you're weak in your arms chances are you're weak everywhere. It's all connected. A good all-over work out routine is probably highly recommended, as juuust doing push ups as a goal alone won't really get you push ups. Your abs and back need to be stronger, your shoulders, and yes, even your legs. It's the reason it's one of the army's more rudimentary of work out exercises. You test physical strength with push ups and sit ups because they require your whole body.
The programs I use actively that I really like:
- Fitness Blender. Free on youtube, lots of modifications and challenges/programs available for super cheap as well.
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Hundred Pushups Also free, I used this when working on my push ups to go into basic training.
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C25K: Couch to 5K Something like this with a couch to 5k plan to help with cardio. There is a lot of other stuff out there (I mostly do fitness blender for cardio + some running here and there) like swimming and biking as well, and plans for that sort of thing too.. but you get the idea.
- Yoga with Adriene .. Free on youtube, great beginner's stretching, and a beginner 30 day challenge.
- Fightmaster Yoga .. Also very free, no equipment necessary, beginner work out challenge + a 90 day one after that + loads of other videos. Yoga if you can get past the preachy aspect of it has some awesome techqniques that will build your upper body strength.
- Betty Rocker.. she posts free youtube videos from time to time, and while I disagree with her diet philosophy, her work outs are easy and fast.
Basically, don't start fast. Don't work out your arms everyday. Build up the different muscles little by little each day.
Iffffff you are a total couch potato (no shame in that) and are juuust starting out.. Start Out very Slow. You don't want to HATE working out.. this has to be a habit formed slowly and sustainably. Rome wasn't built in a day.
I suggest starting out with just setting aside 10 minutes of fitness blender warm up exercises. Yeah, that's it. Do that for about a week or two. Nothing more nothing less. Something so easy you can rush to get it in.
Build it up from there. Try a 5 minute exercise bonus video on top of the 10 minutes. Don't worry about equipment.. just use some old laundry jugs and fill them with water to an appropriate amount to lift for dumbbells and that's it. You don't need any equipment except I'd argue a cheap yoga mat would be beneficial.
After that, focus on flexibility. Flexibility should come before real strength training to me because your muscles tighten up, and the flexibility prevents injury.. so .. now.. 10 minutes warm up, 5-10 minute work out, 10 minutes stretching after. Fitness blender, again, has lots of less than 10 minute stretching videos.
When you can maintain this pattern well enough... Add in a push up routine and a cardio routine. Nothing crazy, you only need a couple minutes to burn out on push ups honestly, and running after that, with stretching still at the end. So, again, bonus burn-out round videos will get you there.. You can try a beginner yoga session one day, a push up day the next, try a bit of walking/running the next, etc. Do different stuff between your warm ups and cool downs. Just keep building up the sessions as you can. If life is busy that day, feel free to drop back down to your 10 minute warm up and-thats-all.. just don't stop altogether. Do 5-10 minutes every single day.. it doesn't have to be impressive all the time. Fitness is a journey.
After about 3 months of this, you'll notice a huge difference in yourself. Just add a little bit more every single week. Arms, legs, abs, cardio, rinse, repeat. Take your rest days though. Stretching is all I do on my rest days. when you very first start out (only doing 10 minutes a day) you won't need rest days.. when you get into it though (working out for 20-50 minutes at a time plus warm ups and cool downs) you will.
You can test how 'ready' you are for the military's PT test. The exact requirements for it are posted online, so you can keep working on it. Really, don't be a hero and go for 100%. I think 70% is all that's needed to pass, so make those your goals. When you're comfortable passing the push ups, sit ups, and run, you're pretty ready for enlisting.. and you can enlist before you go.. Nothing stopping you from starting out with 3-4 months of training, and enlisting as you continue to train.
When I got more fit, I started doing P90X and I really do think that's a very solid work out routine. You can torrent it online pretty easily, it has a very solid way of building up strength and endurance.
This is how I started out, and I'm glad I started out small and slow and not balls to the wall because I would hate fitness if I had started out trying to do an hour everyday. When I got into the army I wasn't exactly in the best shape of my life, but I would have died without training on my own prior to going.
Good luck to ya, there is a Healthy Habits thread for 2017 available as well if you'd like to post your progress on this journey.