What is the best way to secure Laravel/MySQL-API server from hackers?

Everyone we are working in a application. Where backed is laravel 5.1 and database is mysql. Both are under csf firewall and protected from the public. Below is the technology stack :-

Technology :

1) Laravel 5.1 backend Hosting : AWS/ EC2

2) Databse mysql 5.5 Hosting : RDS

3) Fronend Wordpress around 40 sites consuming api from backend.

Currently implemented Security :-

1) CSF firewall on backend.

2) Ip restrictions on RDS.

is there anything else we can do make it secure. Becuase we are saving customer personal and identification details.

Any suggestion will be appreciated.

via Chebli Mohamed