Best securiuty options for wordpress site

I have a client who has 17 sites and they all keep getting hijacked. they use Joomla. It’s my belief the web developer is more of a entry level person than mid-hi level range. After discussing this with my client, I started thinking. I am in the process of putting together an ecommerce site and while i change/edit code, fearless and have no problem taking the time to learn whatever point I am at, I am an entry level person at best.

(long winded) So before I plunge into an ecommercee site, or for any of my other sites for that matter, what precautions should I take for security? I like to think of myself as an intelligent person, but I am no coder/developer.

TIA