YOU SHOULD NOT CYCLE IF:
1. You are under the age of 25
The reason is that your natural test is still very high and you are able to make very good gains without gear. There is also a very good likelyhood that you are going to end up messing up your endocrine system because you are still in a period where it is fluctuating. If you are not making good gains you need to look at your training and nutrition. I personally waited until I was 27 to start taking gear even though I was ready to rock when I was 20 so I know how you feel but you need to trust that with proper diet and training you can make gains naturally. The rare exception is individuals with a lot of training experience in their teens who have already acheived a very high level of physical development (230lbs+) and is already at or near their genetic limit. If you are one of the rare individuals who has already reach a very high level of development through consistent training the absolute earliest you should consider gear is 20.
2. You are over 25 but have been training less than 5 years
If you have not been working your ass off in the gym for at least 5 years naturally with good nutrition you have a lot of natural potential left. It is best to exhaust as much of your natural potential possible before resorting to gear. Gear should be the final piece of the puzzle to your ideal physique. By gearing up too soon you may be short changing yourself.
3. Your diet and training is crap
Gear is not a magical pill. It makes hard work more rewarding, it doesn't give results for doing nothing. All you will get is some temporary water retention which will be gone when your cycle ends. Diet and training on gear is everything. Period. You should have a very good idea of what you are going to eat (including macronutrient breakdown) and what your training plan is going to be. If you aren't already eating properly you can make some very good gains by doing so first naturally. If you aren't already training properly you can make some very good gains naturally...make use of that then think about gear. This site has a wealth of info on both topics. If your training and diet is off you will just waste your money doing a cycle.
4. You are a fat guy looking to get "cut", "ripped", or "shredded"
If you are a big fatso and think gear is going to make you slim and jacked it isn't going to happen. Fatloss comes from proper diet and training. If you can't cut down without the gear you will have just as much trouble on the gear. If you are looking for something to aid fatloss try a fatburner and then add on muscle once you have cut down.
It will look a lot more impressive and be a lot more successful....again this site has a wealth of info on losing fat...I highly recommend checking out the Velocity Diet that Gus is doing in the Physique Clinic...it shows what proper training and dieting can do. The anabolic diet is great for guys, I suggest checking it out as well because if you are fat you are likely fairly insulin resistant so cutting carbs will likely provide very damatic results. You get to eat a lot and because of what you are eating your natural testosterone will be high.
Cutting cycles are run by vets that already know what they are doing, have diet and nutrition down, and are just looking for the last little tweak to their already lean physique. Once you have achevied that status you can look at cutting cycles.
5. You are emotionally unstable
Gear can mess with your emotions. If you are an unhappy/depressed person that thinks being geared up is going to make your life better chances are you are going to feel good for a little while when on and then when you come off you are going to be lower than when you started and likely downright suicidal.
If you are a livewire that goes off in a rage when you drink, do drugs, or when someone pushes your buttons guess what? Gear is going to make this worse. If you have trouble controlling your anger then gear will make it more difficult. You will likely end up acting like a bit of a maniac and alienate your friends.
If you have answered yes to any of the above 5 questions you are not ready for gear.