Sometimes, your site will need some downtime, so you can fix things or update plugins. Most of the time, this tends to be a relatively short period in which Google will most likely not attempt to crawl your website. There are numerous methods you can use to build links some are better for local SEO while other link building methods are geared towards higher organic rankings. Keep your site clean by continually monitoring Google Search Console (formally known as Google Webmaster tools). Like every big task, this one begins with research, too.