Now that you've reached your desired lucidity level, it's time to do, be, make whatever you planned to!

It all starts with remembering your intent - it shouldn't be so hard to remember what you planned to do before going to bed; if it is, you might want to increase your lucidity some more (look for the "Powering up your conscious" section). When you are finally aware of what your goal for today is, remember to take it easy: trying too hard leads nowhere in dreams; instead, worry less and be confident a lot more in your abilities. If you find hard to spawn a certain modification in the dream (like teleporting to a certain place, make something appear, or shapeshifting your body), remember it's taking place in your mind, and as such you can put something in your dream just by thinking it: asking for changes activates related thoughts, or you can just start visualizing the change you want to obtain, and with as much detail as possible (including multiple sensory perception), to both increase the possibility of it happening and the satisfaction with the result.

Of course, if you find the dream fading and getting blurry while doing this, you might want to raise your average awareness of the dreamworld by focusing less on your task and more on what's happening around you, and your sensations.
For getting the task done, you might find more suggestions in the "Grow your confidence" part.

Your task, however, could take longer than expected, and in this situation it is a good advice to check regularly your lucidity level, at least the first times. Do so with quick RC's or other short-term solutions, or remind yourself it's a dream every now and then. Be sure to keep awareness over a minimum level. This is easily obtained by performing impossible actions, like practicing superpowers, or flying, so that they act as a constant reminder that you're dreaming.

When a dream starts to end, you will notice senses fading, visual getting blurry and/or distorted, and losing perception in general. Act quickly! One of the things to do is simply willing the dream to stay, or you could do any of the short-term solutions to regain contact with the dream, particularly touching objects and hanging on to them, as they are dream objects, and as such, you have to stay in the dream to keep a hold of them.

Writerscube posted an insightful advice on this:
Quote Originally Posted by Writerscube
The next time your dream starts to fade, try treating the fading effect as physical matter--it'll make it easier to tear it off of your dream ^_^ and let some light in.
It's what I did when I first discovered how to keep myself in my dreams and not wake up.
1. Dream starts to fade.
2. Tear fade-effect-curtain down.
3. Discard curtain somewhere to the side or in a corner so no one slips on it.
4. A nearby trash can would be the best place to discard Fade-Out-Curtain.
5. (Optional) Sue whoever designed the Fade-Out-Curtain if you ever find him/her ;P I certainly haven't found the culprit for such an outrageous dream inhibiting dream-object so if YOU do, drop a fish market on him/her for me.
More in general, since we are used to interact with physical objects in reality, we can treat events in dreams as such, effectively bending the dream to better fit our customs.
Do you think you can't do that? Then think of when people turn a knob to focus better the dream sight; now why is that, how can that happen? How can a thing such as the entire sight of the dream be related to a (fictional) hand gesture? Besides, that correlation would not at all be a fixed dream property, since one can use tons of other ways to do that, or can use the same knob later (or the same hand gesture, if there wasn't any knob in the first place ;p) to accomplish entirely different feats, such as making the sun rise, or rotating a distant object. So, who decided that pill you're ingesting will help you with your flying skills? It isn't given at all, it could transform you into a bear for all one knows before actually trying. Dreams are the realm of fantasy, afterall.
So, who's really in charge of saying what goes? Think about it. A little hint: you did wish, or command those things to happen before doing them, didn't you?
The answer is, therefore, simple: it is you. This is your dream afterall, you define the rules all the time, unconsciously for the most part. But you can take this process in your hands, and by the time you can create some really advantageous rule, you'd better sieze the opportunity .

Tips

- Taking it all like a game will help a long way - not only you tend to forget about all those concerns this way (and that's a very good thing, since enjoying the dream = keeping it stable, plus the whole fun factor ^^), but it also allows for more mental agility and prowess, the kind that only rapturing moments can draw out of ourselves, and that's quite the best that could happen to you, since it's all taking place in your mind.

- And what after you did what you have planned beforehand? Don't call yourself done yet, there's still so much to do! |) You probably have thought of something else along the way, and you can now get right to it; if you didn't, you still have the other goals you planned to do in your LD; and if there's none left, either take your fun or think of new ones, not even the sky's the limit to what you can accomplish in your dreams! Or, there's always the beautiful dreamscape to explore, remember to take some time for that every now and then ^^

- If for whatever reason, you want to end your LD and wake up, you only have to disengage from it: some go to sleep in the dream, or you could just stop, close your eyes and start wandering with the mind, maybe trying to remember what position you were in while you got asleep. Just remember to do a RC after you woke up, as you could have ended up in a FA!