Assuming that you are going to start smoking there are a few things that you should try to keep in mind.
-No matter what your brain chemistry is, you aren't going to suddenly have cravings like you would within a few months of smoking cigarettes. It is a slowly building psychological dependency. Over a few months you might notice that you are thinking about smoking more and more, and then start smoking a little more frequently. Then, say, six months down the road from then you've bumped it up a little more. You will slowly lose interest in other parts of your life, and start smoking a little more, and so on and so forth. Then, you might make some friends that are doing it all of the time, so you start smoking even more frequently. After awhile of doing this, you will definitely experience cravings, due to building levels of anxiety, although the extent of depression you experience varies widely on your brain chemistry. You should be aware that it is a very slippery slope; if you are going to smoke, try to keep it as small a part of your life, and your thoughts, as possible.
-I would say that twice a week is definitely pushing it, over any long period of time. Smoking that much causes you to have a constant level of THC in your brain, which is something that you have to try to avoid if you don't want to experience negative side effects. If I was going to try to smoke responsibly, I would keep it under once a week, around twice a week or once every three weeks optimally. It isn't the same drug that it was in the seventies; it's much more powerful, and if you want to smoke responsibly you need to adjust the frequency that you smoke accordingly.
-One of the key things to keep in mind is not to accept the status quo of the drug culture. People believe, and will have you believe, that smoking all of the time is acceptable. Not to mention the problems associated with doing this, eventually that kind of thinking can lead you into other, more harmful drugs. It's really a battle of two fronts

ne against your own inclinations, and one against the people around you.
I also want to give you some information based on new research that might steer you away from marijuana use altogether:
- I have talked to two very reputable psychologists about marijuana, and both of them told me that recent studies showed having any THC in your system greatly affects learning ability. At your age you are putting yourself at risk by smoking at any regular interval; you are still learning basic things that you need to know in order to develop fully. I wouldn't want you to jeopardize this.
-With the rising potency of weed it is an increasingly risky thing to do.There hasn't been very much research done about marijuana, and we aren't even close to being fully aware of how it affects the human brain; all we know is that it stimulates certain receptors, especially located in the hippocampus. Your brain isn't fully developed until you are 25, and there has been recent research that shows smoking marijuana before this point retards brain development.
-Smoking pot, as you have probably seen, will add a whole new element to your social life. You will see a whole new side of life, and people, that you have never experienced before. At first it is a very new an enjoyable thing, but as it becomes a regular part of your life, it can be very sad. There is a possibility, no matter how careful you are, that you will get wrapped up in drug culture and have a very bad experience.
- If you are only planning on smoking a little bit, why not wait until you are older and fully developed, when you know you aren't putting yourself at risk?
Ultimately it's up to you. If you are going to do it, just keep in mind that you don't want it to become too big a part of your interests. It's not a healthy thing to get too involved in, like most activities such as sports or music, where the more interested you are the better off you are. It's really the exact opposite.