Flirting in grade school is difficult because one, you don't usually have a lot of time (exception: lunch), and two, you don't want to step on anyone's toes by flirting with someone who's taken. Word travels quickly when you're with the same group of people for years at a time.
So, I'd say that the best way to flirt would be to approach the other person with a compliment; tell them briefly and nonchalantly what you like about their appearance (that day, or in general), or what you liked about one of their school projects (if you're in the same class). It will be an ice-breaker. If you approach the guy with a compliment, the rest of the conversation will seem like flirting regardless of what you're talking about because you went out of your comfort zone to make him feel better about himself. It takes guts, but in the end, it's the easiest way.
you shouldn't flirt just cause everyone else is. trust me. I was in 8th grade last year (and no. you aren't too young) and there were soooo many girls that flirted just for the hell of it. it's stupid. the relationship that comes because of the flirting never lasts and you almost always get heartbroken. and besides. flirting is a natural thing. you can't really learn to flirt. or at least not well. just trust me. it's pointless. and the other kids in the school are only doing it cause "everyone else is". don't follow a trend. set one. it works out for the best. just be yourself. and I know that everything I just said sounds totally cheesy but it's true.
Just get to know them as a friend first. hang out a little so they get used to you. too much flirting at one time is a real turn off. when you start actually flirting keep it simple. touch his arm or twirl your hair. but don't come on to strong. I've found basic works best. take an interest in what he like so talking feels more comfy. make sure you laugh at his jokes, smile and stick to the basics.
by the way, the whole playing hard to get is just a load of crap.
flirting doesn't have to be talking sometimes actions really are louder than words.