Ive had a few lucid dreams, but if i am in an lucid dream, i cant make my own decisions. I always ‘‘go with the flow’’ only knowing that i am dreaming. I also only can chance small things, but i never can fly, for example. Do somebody know how i can become more lucid, so i have (almost) full control?
It has happened to me some times too. I think it has to do with the fact that in the “dream world” we are often confused, i.e. not lucid enough, so we don’t think clearly enough. This means we cannot make clear decisions about what to do or where to go.
For instance, in a couple of dreams I became lucid and aware of the fact that I was dreaming; so I thought “I am going to change this dream”. What happened then? everything became grey and there was nothing anymore because… I didn’t really know what to do. 
I’ve had plenty of lucid dreams and I still get this a lot.
It really depends on what I do the moment I become lucid. Sometimes I take a moment to really STOP whatever I’m doing, and think for a moment on what to do.
And a lot of times I’ll just “go with the flow” and I don’t take control of the dream. Or if I do I do it in minor ways only. It depends a lot on the moment. Sometimes I’m just more aware of the dream state and the possibilities.
It might be a good idea to start thinking about things to do in lucid dreams before you go to sleep (or in the middle of the night after waking up from a dream). Or to resolve that you’ll increase your lucidity or creativity once you do become lucid.
Sven has the right idea- know what you want in an LD. Make a list of goals, imagine yourself doing them and concentrate on them while you perform any LD techniques. The worst thing you can do is go into a dream with no intention. There have been many occasions where I begin to think “well, what now?” and going with the flow is almost always the outcome. I suggest you try to participate in the monthly Quest or the Lucidity Challenge. These give you goals and really help with issues like this.
Thanks for the answers. I`m gonna try the Quests. But I just remembered something: A few days ago I was little lucid, an I tried to open a door by pointing at it and imagine that it get open. Instead, It closed. 
I began thinking: ‘am I really dreaming?’ and I lost the lucidity.
Be more clear about what you want, and know that you might obtain it, whatever it might be. Motivation is always good when wanting to obtain a goal, so write it down a few times, see yourself doing it in your imagination, resolve to complete it, and the dream will come towards your desires and help you accomplish what you issued 
For the control problem, one thing to do is stopping in the middle of the dreams to realize you really are in control. The dream is yours, so you can do whatever you want with it. If you realize the truth of this statement, then the dream is yours, congrats ^^
Since you seem to have the ability to make commands, maybe you should try the technique in which you say aloud “Increase lucidity now!” Or like “Lucidity X10!” Next time if you’re still in the same sort of predicament.
A cool idea someone mentioned, was to tell a DC to keep reminding you that your lucid. In my first LD (2 days ago) i told one to tell me im dreaming. It worked for a little while, until i lost the DC and…you know the rest 