Do you know any tips/interesting articles about how to speed up website on WordPress?

Yet again, do a search on "how to speed up my wordpress site" or similar.
Here's one of the results: http://www.smashingmagazine.com/2014/06/ho...dpress-website/

Hi...

There are several tools for improving the speed...SmushIT for images and W3 Total Cache....
But to really speed up your website...use CDN for images...as images takes a bulk of the downloads...and Minimize the number of plugins....

For word press speed up you need to put less images on web site and also light weight images which loads instantly on word press web site. The main thing is to follow basic flow of word press don't put much content on your web site.

Also for WordPress I would recommend installing one image optimization plugin, here are 3 to choose from:
https://wordpress.org/plugins/shortpixel-image-optimiser/
https://wordpress.org/plugins/kraken-image-optimizer/
https://wordpress.org/plugins/ewww-image-optimizer-cloud/

If you optimize the images before you upload them you need one plugin less.

Yes but you'll have to work more and from my experience the images won't be as small as when using a plugin.

From my experience will be as small as I want them to be.

I was trying to be funny. One person before you suggested fewer plugins. But I still think optimizing before uploading is a good idea.

What image plugin are you using, if any? I have heard that several image slider plugins slow down the entire site.