Welcome to the Q&A Forum

If you only did one thing its Redirects Redirects Redirects. Make sure all your current content has a new home to go to, to maintain traffic. Keep a similar website structure were you can to limit the amount of redirects you have to do. Then monitor search console closely. Any redirects you've missed will 404. Redirect these. Redirect to relevant pages, never redirect a content page to the home page. Maintaining traffic is the priority and this process will do that. Transfer you meta information over to the new site, titles and descriptions etc. Don't overhall your SEO during a site move or it will be hard to identify why traffic is missing if you get any missing traffic. Do the move, wait for things to settle. Then consider your revamping your meta information if you currently plan to. If you're adding new content it gets slightly more complicated but try and compare like for like.

Thanks Christie, Yeah we could start a book with that lot right? Sometimes people just disappear. Others will still be able to search it though and get help.