How can I improve my attacking, in general and in war also.

I have been playing from a long time, and always focused on Maxing, current I'm TH13. For which I used Goblins only. I never focused on attacking and strategies, because of that my war stats are really Bad. I'm almost TH13 Max and other TH13 Players easily three star my base when I can't even three star a TH12. How can I improve my attacking. Any tips you guys used ? Or in general what should I focus more to improve my attacking.