If there was one exercise that is the true test of upper body strength, it would be the pull up. The pull up requires a good body weight to strength ratio, core activation, and practice (hundreds of repetitions). In order to get good at something, you must practice it often. In order to be able to do something, you build up it's components in which is required to perform the task successfully. Fact is a vast majority of individuals in America cannot perform even one single pull up. Why is that? Well, between physical fitness priorities dropping (due to technology, transportation, standards, etc) and obesity (fast food, standards, and lack of knowledge) pull ups are the last thing anyone is prepared for. Sure, you squat everyday with everyday tasks of sitting on your a**, but how many times do you do anything (I MEAN ANYTHING) in your day that builds the muscles in the upper back? Most likely nothing (unless you perform general labor, even then it is minimal). That is why an increased body weight and lack of preparation makes performing your first pull up so difficult. Those new to fitness seem to want to be able to do a pull up. Maybe it is because of the pull up being "cool", or maybe because it is easy to do anywhere. All you literally need to perform a pull up is somewhere to hang. Though individuals find interest in the pull up, they do not know how to go about accomplishing their first one. In order to perform your first pull up you must:
1) Learn scapula retraction: Everyone seems to skip this stage. Hell, even I skipped it at first. Learning to activate the correct muscles is the most important part of any exercise. Sure all guys know how to flex their chest and all girls know how to flex their butt, but no one knows how to activate their back. Anytime I tell someone to use their lats, or flex their back I get this awkward look. When doing pulling exercises without proper muscle activation, you actually incorporate more bicep and less back. This is why many individuals can do heavy/high repetition dumbbell rows and have a s***y back. I usually prescribe 5-10 sets of band pull a parts, 2-5 times a week. The key is frequency and volume, both for mind muscle connection and muscle hypertrophy. I typically angle the band's an specific way to build certain parts of my back. For the sake of the pull up, I want you to do yours not straight ahead, but rather angled 45 degrees up and pull at a diagonal towards your lower chest. This will activate the lats more than if you were doing straight ahead pull-aparts.
2) Reevaluate your body weight: When it comes to body weight exercises, you really want to minimize your weight while having as much muscle as you can. That means staying lean and shedding off the excess body fat. Some body fat is fine, but you may be trying to accomplish a pull up with 45 extra pounds weighing you that much more down.
3) Build the musculature: A bigger muscle has more strength potential than a smaller muscle. Though strength and size have no specific ratio, gaining more muscle will aid in your quest for performing your first pull up. By taking what you learned with muscle activation (doing the pull-aparts), you can perform pull sessions (back workouts) to build up the muscles of your back. This can be done 2-3 times a week for higher volume than the pull a parts. I would typically do 10-15 sets total. These exercises are (but not limited to): latpull-downs, dumbbell rows, barbell rows, and reverse grip pull-downs. Did you see how there is no isolation exercises? That is because we want exercises with the most progressive overload potential in order to build enough strength/hypertrophy to lift yourself up.
4) Develop body awareness/strength: After you have built up the musculature of the back, it is time to get familiar with pull-ups. Instead of dropping everything to only do pull up specific exercises, I would replace the first exercise with pull up negatives. This help the body get used to lifting it's own body weight, helps you develop core stability needed, and gets you mentally ready for a pull up. After you can do 5 sets of 5 negatives, 5 would add some weight and start back at 5 sets of 1-3. This will ensure when you do try your first pull up, you won't be intimidated by the weight of your body.
5) Develop neurological adaptation(practice): After you can perform pull up negatives with some decent weight, it is time for assisted pull ups. Now we always used a partner rather than a band. Why? Well, we didn't know any better honestly, but I wouldn't change a thing. Assistance by a partner is more efficient, because you can adjust the amount of help by communication. With a band you have to adjust the band. If you have a good training partner, they can easily adjust how much they assist you by observing your effort (how hard you are struggling). Build the repetition/set protocol by adding repetitions and decreasing assistance effort (tell them to let you do more of the work). The pull ups will get harder, but you will indeed get stronger.
After taking all 5 steps, it is time for you to get on that bar and perform your first pull up. If you are struggling to get your first pull up, repeat the steps and find where you messed up or skipped. NEVER skip a step. Each step is vital towards your pull up success!