You don't actually need to do both exclusively. You can build strength without particularly effecting the size of your muscles. This is a plus for women especially.
In order to build muscle you have to be prepared to put in hard work! With that hard work you may also see an increase in muscle strength as well as increased size and more definition.
A lot depends on what it is precisely that you want to achieve with your workouts. Do you want to build muscle in order to look good at the beach? Do you simply want to improve your health and fitness? Or perhaps you just want to increase muscle strength to boost your confidence or be better able to protect yourself?
Whatever it is that you want, we can point you in the direction of the resources to help you reach your goals efficiently and, most importantly, safely. So if you want to build muscle read this and the rest of this section.
No matter what the temptation is to build muscles quickly and with little effort, steroids should be avoided at all costs. Not only do the results from the use of steroids vary wildly, but they can be extremely dangerous. It is not uncommon to hear about users suffer from instant, and often fatal, heart attacks, simply from trying to build muscles quickly with little heed to safety. Ok, the boring, safe stuff over, here are some tips on how to bulk up and get beefy!!
If you're looking to just tone your muscles and only build up a little then your best bet is to find a comfortable weight and do a high number of repetitions. You should aim to do around four to five sets of around eighteen to twenty repetitions. The weight should be fairly comfortable, offering only light (but not too light!) resistance. By the time you finish the sets, whichever part of your body it is that you have been exercising should feel a little tired but you should not have reached the point of muscle failure. Because you are not over exerting yourself as such you should be fine to do several different parts of your body with each trip to the gym, but just remember to be careful and if you ever feel exhausted, dizzy, nauseous or overly tired, stop immediately and consult a doctor or, at the very least, a trained professional in physical activity.
If your goal is to really bulk-up then you should do fewer repetitions with a significantly heavier weight. You should aim to do around three to four sets of around eight to twelve repetitions. You should reach the point of muscle fatigue (failure) by the end of your final set. As with any exercise, remember to stay hydrated at all times and drink plenty of liquids.