Magento Performance Enhancement
1. let Magento put session data in database instead of files. Part of configuration to do that in local.xml
2. use global attributes for products if you dont need per view attribute values (admin -> attributes)
3. enable APC or Memcache cache backend and of course enable caching in admin -> cache management
4. enable Mage_Compiler module and disable unneeded modules in admin -> system -> configuration -> advanced
5. Enable Flat Catalog indexing
6. Other useful tips
If you dont have fast connection enough or you want speed up user connections to your Magento you should do few optimalization. You can batch resize product images, or merge and compress CSS files.
6.1. Image size optimalization
You can simply follow tips for resizing images from this How to Article – Resizing images that are too big or too small for the product pages, en-masse. (Tips from this article need linux compatible OS with some basic programms installed.)
6.2. CSS files compression
Open your Magento layout definition XML in your view. And copy all CSS files contents to one css file, and include it instead of multiple files. Then use CSS Compressor to compress CSS files by removing unnecessary space and definitions. There is possibility all files in one will not work together, then you will have to experiment with right combination (eg. reset + menu + clears , boxes , your own … ).
Is used by Magento by default i think, otherwise you should enable it in your Magento administration.
6.4. Gzip / Deflate compression
As written above, you can use PHP gzip output filter, or Apache module mod_deflate. Be noticed, than you can use just one of them
I hope you liked this post, and find it useful.