What is the best approach I could use in teaching science in high school students?

Show some popular movies that have to do with your subject of the day. The kids will think its "cool."

show how things you teach relate to their lives.

Demos and Labs. Science sucks if you cant see it and do it yourself.

WOW...science. Science can be one of the most interesting classes you can take, the teacher isn't BORING. Seriously, it's different than ordinary math, or english, or history. I mean they can all be fascinating, but science always seems so phenominal.

SO..don't screw this up. I mean it.

You can easily lose you're student's interest..right on the first day, and never gain it back.

Best approach, show you're own enthusiasm for the subject, show how passionate you are about it, without being dramatic. Admit that you're a nerd about it if you have to. Speak clear, loud. Don't go for that boring, monotone! Share lots of examples, use demos, show experiements, talk about alot of stories, especially if they're funnie, amusing, scary, or disgusting.

be open-minded to answer any question. don't brush it off like the kid doesn't know anything. you gotta really say something that will catch the kid's interests. research a little, find stuff to tell them that they probably don't know yet, to get them to really engage in you're class.

LASTLY, BE FAIR WITH YOUR GRADING!!

Honesty is the best policy.  Don't try to kid them into thinking you're their best friend,  a mad scientist, or a mean old ogre either.
You're the teacher, they are the students.  You MUST raise their curiosity level to a point where they actually look forward to joining your class.  Amaze them with REALITY.  So many students are stuck in a plastic world.
Be honest with your criticism, be honest with your praise when someone does something WELL.
Good luck.  Either you are a teacher or you are not.

Firstly, you must be interested in science. You must be keen on kindling the interest of students. You must be fully grounded in the concepts.
There is no need to be one up on the students on every issue. It is best to accept lack of knowledge of something they saw on the TV or the news paper and tell them you will explain later. Then make sure you find out and tell them.
Arrange for practicals. Excellent video demonstrations of difficult  or intricate experiments are available. Go through these first, understand fully, and then only show them to the students. They will appreciate your guidance in getting full value from these demos.

Above all prepare each lecture. Even if it is something you have done dozens of times before, it is still the first for the new crop of students.