i hav to compose music for technical vocational training institute

Welcome to my world.  I once composed 50 minutes of music for a video that was nothing but an Electrical Breaker Box with someone's hand pointing to different breakers.
 
Watch some of the "how they are made" tv series.  I think it is available on YouTube.
 
here is my million dollar tip....jump your tonal center (Key) up and down minor thirds.  A minor third change of key does not need to be prepared.  Others do.
 
So, as a general rule,  I go up a minor 3rd when something good happens, down a minor 3rd when something not so good happens.  If I come to a whole new place I go up 2 minor 3rds (a tri-tone)
 
For example...Let's say I'm in the key of G.  Everything is going along nicely, the music is starting to get old and something good occurs On screen.  I jump to Bb.  Then something negative comes along I jump back down to G.  Something else negative comes along I jump down to E.  A scene comes to an end and we open up next to a new day or place...I jump up from E to Bb.
 
This works extremely well if you can avoid using 3rds in your chords or harmony.  You can keep the music sounding neutral without the 3rds.  Major sounds too happy, minor sounds sad.  Power chords that guitar players use all the time work well or substitute with the 2nd or 4th for the 3rd if your chords sound too thin.
 
Congrats, Good Luck and hope I made sense and helped.