The way your content is organized on the page is very important for the success of your SEO strategy.
Most CMS such as Wordpress, Shopify and others, automatically assign URL names (Permalinks) that match the page title, Mobirise doesn't do that and a new page will simply be named "Page-X".
It's very important that the URLs of your website are not that generic, make sure to rename all them so that they match your page title.

Another problem with Mobirise URLs is the ".html" extensions at the end, while this is technically not a problem, but an URL like this really doesn't look good, fortunately you can get rid of the extension by setting up and url rewrite rule in your .htaccess file (remember that .htaccess file is not created by default in Mobirise, you will have to do this manually).

Content is king, that's a very common saying in the world of SEO.
If you are familiar with SEO optimization techniques, you probably know that using a term frequently (but not too frequently) in your page content, will improve the chances to rank higher for that specific term. 
That's important but again you need more than that to get your page to rank in the first page of the SERP (Search Engine Results Page).

Also make sure that your content is easy to read and shareable, also check with tools such as Copyscape, that it is 100% unique: Google hates duplicated content, and using in your website content that has been copied from other websites might even result in a manual penalization of your Website, and therefore in a big drop of traffic to your website.

Meta tags are important markup elements that tell to Google and other search engines important informations about your website.
Meta Titles, Meta keywords and Meta descriptions are the most widely known meta tags.
They are great elements to let search engine crawlers know what your website is about. Meta description is probably the most important, in fact very frequently the Description that shows up in Google search results reflects the meta description of the page.

Meta tag titles, also known as "H1, H2, H3, H4" are used to mark the prority of a title element in the content of your page, H1 is the most important and is usually in the Header, H4 is for a title that is not very relevant, for example it can be used for footer titles.
All tag titles can be implemented in Mobirise through the code editor extension, some of them are set up automatically, however for the best results that's a task that should be done manually.

Image "Alt" tags are also important, they represent the text that is displayed to Google crawler so it should be a short description of what is represented in the image (Crawlers are bots, they can read content but they can't identify what is represented in pictures).

The basic tags are fairly easy to implement in Mobirise:
You can set up a meta description in Mobirise by entering a description in the page settings,
You can also set up an image ALT tag by filling the ALT box in the image settings.

Google Search Console is the most important tool to keep track of your website, make sure to connect your website to it, it will help you keep track of important details about your website, such as inbound backlinks and keywords ranking.
Through the Google Search Console it's also possible to send your sitemap, a sitemap is basically a map of all the Pages in your website, is important to send it to Google and other search engines as soon as your website goes live

Sitemap can easily be created in Mobirise by using the Free SEO extension, you can install it by navigating to the extensions tab in your Mobirise dashboard.

Another tool quite important for SEO is Google Analytics, probably the greatest website visitors tracker, it allows you to see how many people are visiting your website and other important data about your website traffic, so make sure to set it up (You can use the Google Analytics extension as showed in the screenshot below)