Ways to increase Mac speed
Some Mac users have to run 8 to 10 applications all at the  time (and sometimes more). This often makes the mac machine run  sluggish.
Sometimes even  a single restart may fix the issue. When this doesn't speed up mac then  there are a number of things we can do to rejuvinate the mac machine.  Here are few tips I find helpfull for speed up mac without  spending any money.
1. Clean the Startup Items
Some  applications automatically set themselves as a "startup item", and open  at every restart or login. You can find out what is in your startup  items list by navigating to Apple Menu > System Preferences >  Accounts > Login Items. Simply select and remove them carefully.
2. Turn off the applications for  Universal Access, Bluetooth, Speech Recognition,  etc if these are none  of your use.
Putting the unused  applications off saves your RAM and ultimately increase mac speed.  
3. Disable the 'Other' System  Preferences
Please note that in the bottom  section of your System Preferences window there is a label "Other". If  the user doesn't use it often then its suggested to disable it (either  turn it "off" within the Preference Pane itself or remove it from the  folder "~/Library/PreferencePanes").
4. Please Check the 'build' of your software
If  a user is running an Intel Mac, some of the software may be running  under the "Rosetta" translator, which allows to run an applications on  an Intel chip which are built for a PowerPC processor. Note that Rosetta  is of course an efficient tool , but don't use it untill its necessary.  There  are patches for many applications which upgrade them to a  "universal build". By making sure you're running the latest version you  can be confident you're not using Rosetta unnecessarily.
5. Clean out unnecessary code
With  both being options ie; PowerPC or Intel processor, the recent software  come programmed for both. But you don't need optimization for both - you  only need optimization your Mac PC.  There are utilities to strip out  unnecessary code and save hard drive space. 
Editor's note: If a  user is migrating to Intel from PowerPC Mac, he might want to defer  "slimming" the programs until he has made the switch. Otherwise all the  programs slimmed for PowerPC will be running under Rosetta on your Intel  Mac - unless you take the time to do a fresh installation.
6. Get rid of languages and  translations you won't use
There are very  rare chances that a mac user works on different languages other than  than the prefered ones. And even if he does, he can strip out the other  languages not being used and can speed up mac machine.
7. Keep an eye on Activity  Monitor
There are many applications still  sucking up RAM. How can we know about them?  
The Apple's Activity  Monitor, which comes with OS X. tells us about CPU usage, RAM  requirements, virtual memory usage, and whether a given application is a  PowerPC or Intel (Universal) build. Have a regular look of it .  
8. Clean off your hard drive
Usually  we don't clean our trash. Check it today , it may make some hard drive  space free.
Please note that Mac OS X (and the Classic Mac OS,  too) uses the free space on your hard drive as "virtual memory", and it  depends heavily on that virtual memory to run efficiently. If your Mac  PC is running sluggish, that may be due to lack of some required hard  drive. I would suggest to go for Stellar Speedup Mac for ding  this task in a very efficient manner. 
9. Run Speed up Mac   
Its an efficient , fast and affordable mac  utility software for increasing the speed of Mac machine by  removing  all the above unnecessary applications or items.