An entire book could be written on the topic, so we will only provide some quick wins here:

• Get good website hosting!  If using WordPress, you want “Managed WordPress Hosting.”
• Use a valid SSL certificate
• Use a firewall to block spammy IP addresses
• Enforce strong passwords
• Ban users who consistently fail trying to log in using the wrong password or username.
• Ban users who visit too many 404 pages
• If you’re using WordPress, check out our awesome guide on WordPress Maintenance.
• If you’re not well versed in website maintenance, hire a professional who can continually monitor, update, and maintain your site.