Linking all of the content of your site:

 The spiders fetch important data when they're indexing your website and make sure any important content that you wish to appear in Google search results is not missed.

So the first is properly linking all of the content of your site. Let's say you have four pages on your site pages Home, Gallery, About, and Privacy.

Assume "Home" is your main page. Now when a spider visits your site it goes directly to the "Home" page because it's your main page. It will crawl this page and find a link to the page "Gallery".

It will go to the page "Gallery" and start crawling that. When it finds a link to page "About" again it will go to page "About" and crawls it.

But let's say you didn't link the page "Privacy" on the page "About" or any other page. The only way to access the page"Privacy" is to search for it. A bot cannot do both.

Now since the bot never visited the page "Privacy" it's not crawled and thus not stored in the search engine database so it won't be able to appear in search results.

Good practice as always link all the pages on your site. This way the spider goes through your complete site and properly stores each and every page.

Tip: 

Don't put text inside images. Google cannot read text on images so don't put important text inside images.

Spiders cannot read text in images and if you use a lot of important text and images they won't be crawled and will never appear in search results.

Tip: 

Ask Google to call your Web site. Most of the time Google automatically calls your website but there's an option where you can manually submit your website's links to Google. This way your Web site will be crawled faster. 

Search Google Search console, click on the first link shown below:

It'll open up a Website and type in the URL of your website link, check the I am not a robot and when it's done click on submit. That's it. It will crawl your website

Make sure everything on your website is properly linked together.