Flash receives a great deal of criticism from usability and Web standards advocates, but what most critics fail to understand is that the tool is not the problem. Flash can be (and has been) used to create usable sites, if the designer or developer follows these guidelines for usable Flash:

1. Do offers users a choice. Despite very high penetration of the Flash Player, there is still a chance that your users’ browser doesn’t have it and the user doesn’t feel like downloading it. Create an alternate HTML version of the site, which loads fast and gets to the point, and let them choose between plain HTML or Flash. (This is better than using Javascript to detect the plugin because whether someone’s computer is capable of something snazzy doesn’t necessarily mean the users wants to see it that way.) Also, be sure to include a graphic and a text link directing users to the page where they can download the plugin.
2. Do offer the option to turn off the sound. Flash compresses and streams sound files but sound files in Flash movies add bulk. Treat sound as an enhancement, not the main attraction. Let your users turn it off. And when testing the movie, turn off the volume to make sure the message is clear and understandable without it.
3. Don’t use Flash for an intro animation. Clients may still be asking for it, but this Web design technique is completely outdated -- not to mention not at all user-friendly. If they insist, you can put the animation in an optional window that gives users the option to play or not. Also, place a 'skip' link in your intro and give them access to it before the movie loads or while it is loading.
4. Do keep them entertained while they’re waiting. Downloading is almost inevitable with Flash, especially if the user is on a dial up connection (which many still are), so if you must keep them waiting, don’t let them wait idly in the dark. Give them a game to play, something to read, something to learn. Also, tell them how long the download will take by showing the classic 'loading' or progress bar. Otherwise, they may think the site is broken or stalled.
5. Don’t get rid of the Back button. Because a Flash site is a stream of animation and not a series of pages, like an html site, the “Back” button isn’t organic to it.  However, the Back button is the most popular navigation element on the Internet. It’s on all standard browsers and looks pretty much the same from browser to browser, so everyone is familiar with it. That’s why, when it disappears, users become easily disoriented. Flash allows you to build a Back button to simulate the familiar experience of an html site and it’s a good idea to do so.
6. Do allow for keyboard navigation. Users with mobility disabilities and repetitive stress injuries use the keyboard to navigate. So make sure Flash elements have keyboard accessibility. And be sure to descriptively name all navigation, graphics and linking elements so that those with visual impairments using readers and search tools don’t think the site is empty.
7. Do use Flash's small, anti-aliased text for short blurbs or captions. Use other media, like HTML, for large amounts of text.
8. Do choose vector imagesover bitmap images because they use less memory.