Increase download speed

You want to download faster?

OK, just make sure that
you use Good settings for high download speed
you don't have a NAT problem
you don't use a standard incoming listen port like 6881
you use Good Torrents
you do NOT use Force Start

When you are using a Windows OS you can also use the TCP Optimizer to optimize several system settings for your line speed.

Just click all those links and read the info carefully... after reading that you may ask questions about that topic in the IRC channel.

Another user complete download = faster download for you

Another reason for uploading is simply to help fill everyone up. By doing this you prevent someone, who is seeding, trying to upload a part you already have (and which is useless for you). The chance that he then uploads a piece you need becomes greater. This will not result directly in increasing speed but it will optimize the uploader's upload which results in you getting your piece sooner since you no longer need to wait for a piece. Think of it as a reverse Zero Sum game.
[edit]
Use new Azureus version

Newer Azureus versions, begining with 2.3.0.7 Beta 19, include all-new completely re-written piece picking code that will generally reduce the time to complete torrents.

The Azureus Beta page is here.
[edit]
More Things To Know

It is very important to know that, when you are seeding, or uploading a torrent, the u/l speed of your sharing is not the only thing using your upstream bandwidth. Requests made to the tracker, browser requests to load web pages, and sending email all utilise your upstream capacity. So you may experience the following difficulties when running Azureus.
"Unable to locate server..." error message whilst browsing the web
Connection problems
Other web related issues

If you find yourself having problems with the Internet while Azureus is running, try further lowering your max upload.

The point of this section is to explain that when configuring your maximum u/l setting in Azureus, it is best not to set it to use all of your upstream capacity. Rather, it is best to set it to use a maximum of 80% of your total upstream bandwidth.
[edit]
A note on ADSL speeds using PPPoE:

An ADSL connection using PPPoE has reduced usable bandwidth compared to the theoretical bandwidth that is purchased. In my experience a theoretical 512kb/s dl product has overheads due to the PPPoE encapsulation that limits the connection to about 400kb/s max. This means the limit before applying the suggestions above should be 400/512 ≈ 78% of the theoretical bandwidth. This logic applies in both directions. So Azureus DL max would be:

80% × 78% × 512kb/s ≈ 319kb/s; 319kb/s ÷ 8 B/b ≈ 40 kB/s if Azureus is the only Internet application. Reduce this somewhat to allow other Internet protocols better response on the same connection.
[edit]
A tip for RcvWin/TcpWindowSize tweakers

"I've most often seen [poor performance] with people running on Windows who 'tweak' their TCP send and receive buffers to be very large in search of higher bandwidth. Buffered data is obsolete data and causes serious problems in the responsiveness of the protocol to changes in the peer state. Since data and requests share the same TCP socket, buffering lots of data means that your request for a block may have to wait 10's of seconds before it even gets transmitted, by which time the peer you are talking to may have decided that you aren't interested in his data after all, or your own client may decide that the peer you are talking to is snubbing you. Either of these is disastrous to download rates."
taken from the BitTorrent developer mailing list
[edit]
Final Note:

Trackers get uncountable numbers of requests made on them every day. I have seen that some people think that clicking on the "Manual Update" button will somehow increase their speeds or make an offline tracker come back online quicker. It Will Not. Clicking on the Manual Update button is for last resort checking when there is a connection problem On Your End. For example, if you are using a proxy for your tracker requests, you may need to perform some manual announces to verify that the proxy is working while you play with the settings. Also, some private trackers require peers to be logged in on their web page before they can connect to the tracker, adding the IP they logged in from to a whitelist. In this case it may be necessary to announce manually after you log in.

In any case, the more you click on the Manual Update button, the more this will destabilize the tracker, and cause it to go offline for everybody. So for the most part, Leave the Manual Update button alone, and your speeds will recover by themselves (unless there are other issues, but anyway, this button will not help to fix those either).