Firstly take a deep breath, that really excited lifting feeling you get in your stomach, get rid of it,
Then you need to start by becoming more adjusted to the dream world and your position in it, rubbing around your body and the floor and walls or anything close-by will get your senses adjusting to the dream which will keep you in the dream and in control and help to make the dream more vivid, when you think you're vivid enough start to do what you wish.
If you still start to feel like your waking up during the dream spin on the spot and imagine a place or a person or something to change your surroundings, rub your hands together is always a good technique.

Sometimes when your lucid you may get frustrated because you know your lucid and say for example you want to fly, but you cant.
I use a mantra repeating to myself over and over "this is my dream, i am in complete control" or something similar, mix it up if u wish say "i can do whatever the FU** i want" or something, if you still cant fly try to use a sort of physical means of flying, one time i grew wings on myself and it helped. Maybe think to yourself "i will turn round and a controllable flying carpet will be there" and expect it to be there.

You can use things like that in your imagination to help you as you learn to trust how much control you have within your dream. there is a word or actual term when you use something as a physical means of doing something you want in an LD i cant remember what the term was but you get the picture i guess.

You can even do things like pull a remote from your pocket which when u press pause it pauses people or the dream world (like in the film click) etc.

have fun LD'ing.

The main key of staying within the dream though is activating your senses to the dream world around you to deepen your visuality and awareness of it. To make logical sense of what's there without coming over excited.