You can disable services that you do not use or use only rarely... e.g. I usually disable printing and bluetooth. You can do this using the 'sysv-rc-conf' command line tool. If you don't know what a service is from the name, just search on google or for the package in synaptic and it will tell you. Run 'sudo sysv-rc-conf' and move around with the cursor keys and enable/disable services using the space bar. To disable, uncheck all boxes for a specific service. You can always start a service when you need it. e.g. to start bluetooth run 'sudo /etc/init.d/bluetooth start'
You can also comment out apps that you do not need from the fluxbox startup file... ~/.fluxbox/startup . Just add a # at the beginning of a line to disable the app.
You can use preload to get an extra performance boost. http://www.howtoforge.com/speed-up-your ... buntu-9.04
Increasing swap is only useful if it gets filled up. You can see how full it is by running 'free' in the terminal. If you are talking about hardware, getting a better CPU and more RAM will give you better performance... but you didn't need me to tell you that