Since i always have school in the morning,i can’t really afford to wake up in the middle of the night,or have naps in the afternoon,what technique would you recommend for me?
Thanks 
first of all: regular Reality Checks, ask yourself if you are dreaming, how you got there, etc.
then MILD while falling asleep, here’s a tutorial:
https://community.ld4all.com/t/mild-tutorial-mnemonic-induced-lucid-dream/29018
it works better if combined with WBTB, but i think it will show results thatway, too.
hope you find it useful 
Your situation might not be the best for general induction techniques but don’t look at that as and disadvantage. Keep in mind that induction techniques are the core of lucid dreaming. Awareness and lucidness is.
You being in school half a day and having other activities after school is great, it’s not that strict as a job so you can do all types of awareness techniques/exercises…
Like noobdreamer suggested, RC’ing is the easiest way to raise your awareness. Then practicing ADA or LL is also great. Always start small, easy and with time you’ll can use more and more exercises for awareness and in no time you will become lucid in dream. But patience is needed.
You can also squeeze meditation in your schedule if you have time. 5 or 10 minutes peer day makes wonders.
Good luck!
Introduce an afternoon nap to your schedule. It won’t really mess it up, and you get REM sleep on those naps.