Dirt Rider Magazine

2nd gear. Clutch on the verge of exploding and release it (smooth and steady tho dont panic) while again smoothly but quickly hammerin on the throttle. And jab ur clutch to upshift and brake at the VERY last second

lol its ok. Its just a stupid theory i have in my head

As Maple said and as you bring your feet up shift to 3rd and you will pull away from the pack. Lots of gas.

Take it or leave it jake. Dont b a dik

I should have said that ML because that is important shifting with the heal. Its the only way to do it with speed and the  best way.

There are a lot of good starters in the pros I really like what Villipoto does if you can watch some of RC's or McGrath's videos they really were good with the fundamentals. 
The Gary Semics GSMXS.com starts video is very good.

Keep both feet on the ground for the start this helps keep you balanced.
2nd gear for 250 or bigger, 1st for small bore
To elaborate on NZ's if it is tacky dirt you need to be up over the bars the more the traction decreases the more upright you can sit
you need the weight over the rear tire to help prevent spinning.  With concrete you can sit upright
As you release the clutch/apply throttle pull yourself forcefully to the bars with your arms and abs your head should be over the number plate.
As far as clutch and power before the gate drops the power should be clean not over revving but high enough not to bog as you release the clutch.  As the gate drops open the throttle all the way and use the clutch to control wheel spin and front end height.  Ideally the front wheel should be approx 3 inches off the ground until you shift.

As mentioned by pop and ML as the left leg is lifted to the peg click to third with the heel of your boot  Keep the throttle pegged during this shift   I don't use the clutch for this shift any reduction in power or traction and the field will fly by.
A Stars started putting a little logo nob on the heel back in the 90's just for this purpose many others have followed suit.  (The mid 90's Tech 7 was the first boot I can recall having the nob someone else may have had it before them but not that I can recall)

Practice Practice Practice.
If the engine bogs or you go over the back you are letting the clutch out to fast for the dirt.
Work on clutch control and balance.

yeah. thanks i really need to work on my starts. i have been starting in 2nd in my 150 and it seems fine, but i will try first. at my first race i was about the fourth to the first tun, out of 9 or 10 people. so i didnt do that bad, but i really would like to be the first one. mike alessi once said "the start is the only time you can pass everyone at once".

sorry mark pretty much covered it, i didnt read all of the posts.

nah. IMO powershifting really isnt bad for your bike like some people think.

I do not use the clutch on starts and when down shifting into corners.

If your tranny wont power shift on the start then a quick slap of the clutch is MUCH better than letting of the throttle
For down shifting specifically going into turns I never to pull the clutch unless doing a brake slide.
The back end tracks much better and is more stable, less likely to kick if the engine is helping out.
Once in the corner I will start slipping the clutch if needed to control traction while keeping the RPM's up.
Coming out of a corner is just like a start throttle pinned use the clutch for traction control.
(I work a lot on corners trying to control the back end with the clutch, the response is so much better doing this instead of waiting on the engine to respond) 
The other technique for corners that I try to incorporate into practice is dragging the front brake in a berm or rut this will compress the front end which in turn shortens wheel base and increases the steering angle which lets you carry more speed through the turn.  You don't always need to do this but It will keep you in the rut or berm if you are a little hot coming in or trigger happy on the gas.

You may need to replace brakes or clutch a bit more often with these techniques but the tranny will hold up no problems.
You will also go much faster....
This was a bit more than what you were asking but hope it helps.  Please note my reference is 2 strokes with four stroke there may be a little different technique.