what you will need to do is create .htaccess file.
in that file you will need to write
php_flag zlib.output_compression Onand save it to your /public_html/ folder
this will compress all your php files
for your scrypt.css you will need to change it to a .php file and add at the beginning
|Sry i can't figure out how to add code to blogspot with out it messing things up|
and make sure to change your .css extension in your header in your php files.
this will help speed up your website by compressing the data so that the visitors will have to download less.
this will not help speed up your photos or compress them. so still use a small photo format and use thumbs where ever posible to help speed up your website.
also some news is google is developing a photo format that they hope to take on jpg and png for web photo format
it is called right now WebP
for more information on that you can check out