Flash Games Studio:

I contributed a chapter (chapter 7) to the book Flash Games Studio
published by Friends of ED.

You can find out more information about the book from the friends of ed web site.

The chapter I wrote provides an overview on building a platform game in flash. The game described can be found here: rescue run
The chapter also covers building a level editor for the platform game.

Source code: the source code for the book is available here.
For some reason my source code isnt online at the moment so you can get it here.

A sample chapter by Glen Rhodes is available here.

Help: if you have problems with the chapter you can email me at david@artifactinteractive.com.au

If you find the game is running a bit slow Ive provided some hints here:

Speed

One of the biggest issues for game development in Flash is speed. You can set your flash file to run at a frame rate of 25 frames per second but there is no guarantee that the flash player will actually run at that speed. The flash player tries to run at the specified frame rate but it will often slow down to a lesser frame rate if it is trying to do too many intensive tasks at once. The result is that your game may run slowly and a slow scrolling platform game isn't a lot of fun.

Let's look at some of the things that slow the flash player down and how you can avoid them.

Large graphics
The Flash player will run slower if it has to manage the movement of lots of large graphics. If you use large graphics for the platforms in 'Rescue Run' you will find that the game slows down. Keep all of the graphics as small as possible.

Lots of movie clips
It's a general rule that the more movie clips you have moving around the slower the flash player will run. In 'Rescue Run' you may notice the game slowing down if you build long and complex levels. The solution is to have lots of short levels instead of a few long levels. You may also consider removing the background scrolling mountains, as this is not critical to the game and may slow the game engine down if you also have complex levels with large graphics.

Transparency and gradients
The flash player has to work harder to render graphics with transparency settings and gradients. Wherever possible avoid using graphics with alpha settings or graphics that contain large gradient fills.

Complex vector graphics
Even though flash is a vector based program it can some times slow down slightly when rendering complex vector graphics, especially graphics with lots of small gradient fills. You will sometimes find that the flash player performs faster if you use a bitmap graphic in the place of a complex vector graphic. For example, if you create a complex vector background graphic to replace the mountains in 'Rescue Run' you may find that the game slows down. The solution is to export your vector background graphic as a png image and then import this png image back into flash and use that instead of the vector graphic.

High Quality
The flash player will run faster if you set the publish settings to low quality. You may not like low quality because your vector graphics and text will look ugly and jagged. However try running 'Rescue Run' at low quality. The player and text look terrible, but the rest of the game looks much the same. This is because most of the game elements are bitmap graphics and at low quality bitmap graphics appear almost the same as at higher settings. If you build a game that uses only bitmap graphics then you may find that it looks good enough to run the game at low quality. The ugly text that you find at low quality can be resolved by changing the text font to a system font such as _sans.

Coding
The complexity and style of coding can affect the speed of a flash game. The code in 'Rescue Run' has been written to ensure that the game runs as fast as possible while also being easy to adapt and understand. An example of coding that has been written in a specific way to speed the game up is the platform collision detection. We check for a collision between the platforms movie clip instead of testing for a collision against each and every individual platform. This is less code for the flash player to perform and hence runs faster.

One coding trick that can sometimes speed up flash files is to change code that is repeated frequently back to flash 4 style syntax. Flash 4 style syntax actually runs slightly faster in the flash 5 player than the equivalent flash 5 syntax. So sometimes you will notice an improvement if you go back to using tell target to control movie clips, set Property to set properties and slash notation instead of dot notation. However you should be aware that Macromedia have said that the flash 4 syntax is depreciated and may not be supported in future versions of the flash player - so only use flash 4 syntax if you really need to try and find every little extra speed boost.

Full Screen
Even though flash movies can scale to fill the browser that doesn't mean you should set your games to 100%. The larger the flash game is the slower it will run. So keep your games as small as possible to keep them running at an optimum speed.

The above list shouldn't been seen as a set of rules but rather guidelines that will hopefully give you a start on how to modify your game if it isn't running as fast as you would like.

You should also be aware that there are some things that may effect the speed of game that you cant control, such as the speed of the users computer and if the user has any other browser windows open. In this case the best you can do is recommend to your users that they close all other browser windows and provide minimum hardware specifications for the game. You may also may want to offer users on low end computers a button that switches the game to low quality or turns off the games scenery (such as the background mountains and sky), which should make the game run faster even though it may not look quite as nice.

link: some more advanced coding techniques for speed optimization