Crucial tips to increase Page speed

I'm working on a site where Dev's only have WordPress knowledge and are in learning process. So, they find difficulty in finding problems and correcting it to increase page speed. Here's what we done so far,

1.Lowered image sizes below 150kb in banners and others below 100kb 2.Installed Litecache plugin (it helps to a great extent)
3.Switched hosting server to Cloudfare 4.Deleted unused plugins

What else I need to do?