Going through you list one at a time. (Its really 4 questions at least)
Im using a class I named "GlobalVariables". I use this for like have
a "Speed", that I can reach everywhere. So if im on the main line
or, in a class I can type "GlobalVarialbes.Speed" and then change
the speed. Is that a good way of handle stuff? Or does it get heavy
for the preformance to do this? I just kinda of many of these
"globalvariables".
Using global variables and function calls can take some time. If you use the variable more than once within a method, you can optimize slightly by caching the value to a local variable. But be sure to test the outcome, as caching the object if it is not a primitive value can cause a "new Something()" constructor to be called which is very slow.
One REALLY annoying thing is that when objects move, I really need
the FPS to be 60 FPS. Because if the FPS is around 30-40, the
objects doesnt move at the same speed, and the objects seems to be
alot closer the each other to... This is really annoying. I just use
object.x += GlobalVariables.Speed (Speed is maybe 4)... Any
suggestions here?
Change the way you think about speed, from pixels per frame, to pixels per second. Then use getTimer() each second to find out what percent of a second has passed since the last rendered frame. I put some example code in this thread here: Frame skipping on Flash
If I use a background it actually takes alot of the FPS from me.
Around 7-10 fps. How can I make a background picture less
preformance eating?
Backgrounds, and drawing in general will be costly operations. Use cacheAsBitmap if the background does not scroll. Be sure the background contains no child layers if possible. Use a bitmap and not vectors. And keep it as small as possible - do not have extra bits off screen. Also- make sure the background is not being scaled. Turn off bitmap smoothing too. Try setting you stage quality to StageQuality.LOW, or StageQuality.Medium and see if that helps.
==UPDATE==
Now that AIR 3.2 is out and it supports OpenGL on iOS and android, use that feature. Its called "stage3D" in flash and it is really the only good way to do your graphics for mobile with flash. For 2D graphics out the starling framework. http://gamua.com/starling/ It's the same engine used by Angry Birds on Facebook. So its real-world tested and production ready. (And its open source!)
General tips maybe? I use the GPU mode on the iOS devies :)
General tips: use bitmaps for everything. Avoid transparency whenever possible. Do not use filters, or blend modes. Avoid Alpha tweening. Avoid creating new objects - recycle commonly used objects, especially display objects. Remember that adding and removing children is also costly. If you have a bunch of bullets in a re-usable bullet pool, you can set them to visible=false. Then visible=true when you re-initialize that bullet object. Try a search for "AS3 Object Pooling"
Use Vector instead of Array.
And Finally: Test and re-test. Measure the time of each function call. Optimizing flash is a deep and rich topic - its one that you will never exhaust. In part because your mileage will vary from project to project. Here is a good link to get you started on learing Optimization techniques for AS3 http://drawlogic.com/2009/05/22/as3-flash-efficient-code-techniques-vectors-in-flash-10-faster-jpeg-encoding-other-optimization-notes/
