I’ve been doing SEO for over 20 years and I will list some things that you can do for your existing site, maybe its a new site or maybe its an old site that either has no traffic or once had good traffic and has died out for one reason or another.
One thing you can and should be doing is running PPC campaigns as you should always have both organic and PPC campaigns going on.
Do you need a quality backlink to reinforce your search terms?
A word of caution you need to be careful about backlinking manipulations as they can result in search penalties or even outright bans. See the thing is if you get a link on quality popular relevant site it would boost your site up tremendously and reinforce the niche search term but the issue is sometimes you can’t always get a link on the high ranking industry niche site and sometimes it is often really hard to find good links to get and you start all of a sudden posting backlinks and google flags it because the links are questionable and if your competitors or google auditors catch you they can penalize your domain.
What you need is a good quality-related link if you can think of any yourself. I know of customers who have gotten penalties from there SEO people backlinking because they are not an industry expert in your field and cant come up with the ideas of where to get good relevant links at and the inexperienced SEO person puts up links in link farms and easy to get links and that gets you in trouble.
But even more beneficial than the backlinks because it brings immediate customers to the site is just do PPC and PPC traffic will accelerate your analytics for any other changes you make to the site, there is a cost to this but honestly, you can’t always get high-quality industry niche backlinks.
If you also at one time posted blogs and pics in galleries you did and you need to keep doing that or the content and site traffic will die down. When a customer asks you a question turn the response into a blog and each new service you do post pics on your site in your gallery to keep the content fresh and relevant for traffic.
Also if you are not dropping in ranks because you need a good quality backlink on a relevant site to reinforce your niche terms then very often if your site design is over 4 years old the site may drop out of the results and not until new content and a new design is posted do they come back, also the new design triggers analytics rescoring on the pages which can put you back in the ranks if your content and design is fresh and you have made text improvements to the site.
Also, I will be honest with you WordPress has much more development occurring for it with the latest technology and plugins it tends to outrank because its easier to implement things that the search engines score high on like performance-wise and it has design-builders that make it easier to create higher UX scores. You may want to migrate your site to WordPress and use a builder like Divi in addition to the things I mentioned earlier.
You can get pretty cheap clicks on Bing Ads https://bingads.microsoft.com/ . I don’t know if I would put any effort into social media ads they are very expensive and with those kinds of social media ads, you are trying to find your customer out of everybody and entice them to buy whereas search engine marketing people are looking for you but this all depends on what you are selling some products do well as enticement type sales.
Also, you need to be descriptive on your description ie. use descriptors and make sure on the page does the search term appear in the description and meta descriptions, these kinds of onsite text changes can bring in a lot of traffic as well.
If you had a blog, you need to post some new posts I would only blog about questions people ask like is this coating better than this coating etc. Make sure what you post is relevant and will bring in traffic that will convert the most, having a bunch of traffic that doest lend to sales just puts a load on your hosting costs.
Maybe most all your prior SEO efforts are missing meta tags or meta tags that are targeted/tagged for search. You should have the meta descriptions as well as some text on the page with the same and a bit more descriptive text but in addition, you need at new blog posts and it needs to have done to all your pages to go around and update targeted meta descriptions and page text.
You also need to make sure all your websites are fast and without error and any sites that may be affected by outdated designs updated with new designs.
You want to write down keywords you would use to find your products/services on the search engines and you want to make sure that you can target them on your site organically and you also want to target those keyphrases for PPC because the PPC will accelerate the showing of your site for those terms and build the analytics much faster as well as the scoring faster and the changes that you do make are all taken into consideration much faster with the search engines when you are also running PPC campaigns. When you are running ppc campaigns you are more favoured to show organically across all engines.
But you need to be careful with backlinks unless its a high-quality link like for me creating a Joomla plugin and putting it on joomla.org gets me a link and a good link but if I try to put a link on less relevant or iffy type sites the search engines have ways of guessing if you are attempting to manipulate its results and can actually harm you more then do any good.