I'll try my best to explain some stuff. The first poster is correct is saying that you must understand what each wave is. The p wave deals with atrial depolarization, QRS complex is ventricular depolarization, and the T wave is ventricular repolarization.
There are several things you are looking at when reading a strip. First, the seconds. It's done in 6 second strips. There's 30 big blocks in a 6 second strip, which at the top of the strip there will be 3 long lines in the 6 seconds. The first thing you have to decide is if the rhythm is regular. Look at the R part of the QRS complex. Take a paper and mark where each R is and see if they are equal. If they are, it's regular; if not it's irregular. Second, look at the heart rate. You get this from counting each R in the 6 second strip and multiplying by 10. Third, look at the PR interval. It's the length of the p wave right before the QRS complex. It's supposed to be 0.10-0.20 sec. It's approx. the equivalent of two and a half tiny boxes. The thinner it is, the lower the sec. Fourth, look at the QRS complex. It's supposed to be 0.04-0.12 sec. The same with the QRS complex, the thinner it is the lower the sec. and the longer it is the higher the seconds.
Then, you have to interpret the strip based on those things.
There are many possibilities. Some basic ones are: normal sinus rhythm (regular rhythm, normal HR which is 60-100, normal PR interval and normal QRS complex); sinus bradycardia (regular rhythm, below 60 bpm heart rate, normal PR interval, normal QRS complex sec); sinus tachycardia (regular rhythm, 101-150 HR, normal PR interval, normal QRS complex sec); Supraventricular tachycardia-SVT (regular rhythm, 151-250 or greater bpm, normal PR interval and normal QRS complex sec.; the p wave may be present and normal or it may be within the T wave due to the high number of contractions); atrial flutter (rhythm is regular, HR- there's the atrial HR and Ventricular HR. Atrial HR is high due to the "f" waves and the HR based on the R wave can be normal or not; like I mentioned, there are "f" waves which the f stands for flutter and they look saw toothed and there are multiple "f" waves per QRS complex; QRS complex sec are normal); atrial fibrillation (rhythm is irregular, HR can vary, no "p" wave or it will look like little squiggles, and there is a present QRS complex and T wave; there is no "p" wave due to the fact in A. Fib the atria quiver instead of contracting); Ventricular tachycardia (regular rhythm; increased HR--obviously because it's tachycardia, no "p" wave, QRS complex present but longer than the normal 0.04-0.12 sec); Ventricular Fibrillation (rhythm unmeasurable; HR is 0; PR interval and QRS complex unmeasurable; there's coarse and fine. Coarse has higher waves than fine. Both just look like scribbles and non-readable waves); asystole (unmeasurable rhythm, HR is 0, unmeasurable PR interval and QRS complex; just a straight line or wavy line) There are many other rhythms; then there is what's called a PVC (no "p" wave and the QRS complex is longer than 0.12 sec; happens within an underlying rhythm; either unifocal or multifocal. Unifocal means there is only one site of origin and multifocal means there's multi sites of origin. If there are two unifocal PVCs then they will look the same; two multifocal PVCs look different from each other. There's also the pattern of the PVC: bigeminy which is every other complex is a PVC, trigeminy which is every third complex is a PVC, or quadriminy which is every fourth complex is a PVC; if two PVCs happen right after the other without a complex of the underlying rhythm in between, it is a couplet. That's the basics of PVCs.)
How you treat the dysrhythmia depends on what it is and whether or not the pt is symptomatic/unstable. Assuming you treat them; all of them get oxygen. Sinus bradycardia is treated with atropine (anticholinergic that increases HR); sinus tachycardia depends on what it is from-- fear/anxiety is usually something like Ativan/calming techniques, hypovolemia is fluids like NS and LR and D5W, etc.; SVT is calcium channel blocker, syn. cardioversion, and lowering the HR with valsalva manuever; A flutter is cardioversion and calcium channel blocker; the same with Atrial Fib. and they can also require a pacemaker (think about it-- the SA node is in the right atria, so anything with the atria or involving the SA node can get to the point of requiring a pacemaker); V. Fib is CPR, defibrillator, lidocaine, and epinephrine and V tachycardia depends on whether it's pulseless/unstable. If it is then it's CPR, defibrillator/cardioversion, lidocaine, epi....the whole nine yards LOL. Stable is cardioversion. Asystole or pulseless electrical activity (PEA) is CPR and lidocaine/epi. Do not shock asystole!!!! It can damage the myocardium. Pulseless Electrical Activity means there's activity on the monitor but the pt has no pulse. So, make sure you treat the pt and not the monitor.
I hope this helps. I am not a nurse yet (take boards this week) but I find EKG strips interesting and have been looking at them and will eventually take an offical EKG class when I get money. But those are the things you have to consider looking at a strip and when you look at the treatment.