The key to longer lucids is remaining calm and keeping the dream stable. You can have all the fun you want, but try and keep your emotions under control as much as possible. Many dreamers become lucid and then try to hurry up and get as much done as possible before the dream ends. This "racing the clock" technique can lead to consistently shorter lucids. Just stay calm and go about your dream in an experienced manner.

Upon becoming lucid, perform some stabilization techniques (even if it already seems stabile). Then every few minutes or so during your dream perform a qucik stabilization technique to keep the dream stabile (even if it seems stabile at the time). I, personally, like to perform a nose pinch RC for stabilization throughout the dream (RCs can be a great way to stabilize along with many other techniques). Its quick, easy, and can help prolong the dream. Another key is to not think/fear/worry about waking up. This can be difficult sometimes, but I find that staying active and engaging in dream activity can help keep your mind off waking up.

It'll take some practice to get used to extending lucids, but just keep trying and working on that extension. Your hard work will pay off. I can consistently have 30+ minute lucids, with plenty of hour+ long lucids mixed in. It is possible, but it just takes some work and practice.