Here you can find some tips to make your store faster. Please add comments below if you have anything to add.
optimize your images
The most common problem with slow stores is huge images inserted into all pages (logo for example). If your main image is larger than 10-15kb - you may consider optimizing it. If your product thumbnails are larger than 10kb in file size - with 10 products on the page you are looking at 150kb page, which will be slow for people on dial up modems.
clean your statistics in your store's database regularly
Statistical data can take up to 90% of your store's database, which can considerably slow down your store if you do not clean it from time to time. To do so:
Backup database first : go to "Control panel" -> DB Backup/Restore -> click [Generate SQL file]
To clean Statistics : go to "Control panel" -> "Summary" -> scroll down to "Statistics clearing" -> select data you want to clean -> [Apply]
compile_check = false
If you are comfortable with using FTP to change your template, you may consider this to add some more speed to your store. This tells Smarty whether to check for recompiling or not. Recompiling does not need to happen unless a template or config file is changed. Typically you enable this during development, and disable for production. Login via FTP into your store account, go to "store/Smarty-2.6.3" folder, find "Smarty.class.php" file.
var $compile_check = true;
var $compile_check = false;