The scope of this question is too vast to be answered in a few lines :)
However, there are few thumb-rules your should definitely follow:
1) Optimize your images
2)Use proper coding
4) Cut short on unnecessary plugins that take too much time to load
5)Use your server location wisely.
You should also keep checking your website speed with some great free tools like Google PageSpeed Insights https://developers.google.com/speed/pagespeed/
and Pingdom http://tools.pingdom.com/fpt/
and keep doing the changes suggested by them.
Also see if this recent blog post by us helps : 5 Simple and Easy Tips to Increase Website Speed https://blog.znetlive.com/5-simple-and-easy-tips-to-increase-website-speed/
Did my answer help you?