to avoid throwing link equity away, you might create HIGH-LEVEL IN-DEPTH TOPIC PAGES on your site and redirect (or use canonical redirects) any related expired content that HAVE INCOMING BACKLINKS, to this topic page (and keep it updated, folding content from old pages, where relevant and there is traffic opportunity, to create TOPIC pages that are focused on the customer e.g. information pages)
Great SEO is increasingly dependent on having a website with a great user experience. To make your user experience great requires carefully tracking what people do so that you always know where to improve. But what do you track? In this 15-minute talk, I’ll cover three effective and advanced ways to use event tracking in Google Analytics to understand a website's user.

I was used to work with Tools like Sistrix, Ahrefs or Searchmetrics and did not know about SE Ranking before. But those tools were too cost-intensive for a small and quick start into SEO so I tried it out and I am quite satisfied with it. I like the ability to pay for certain services with credits, as I am not using them on a very frequent level, so it actually gives me greater flexibility to only use them when needed and not paying for them even when not using them.
QUOTE: “An infinite number of niches are waiting for someone to claim them. I’d ask yourself where you want to be, and see if you can find a path from a tiny specific niche to a slightly bigger niche and so on, all the way to your desired goal. Sometimes it’s easier to take a series of smaller steps instead of jumping to your final goal in one leap.” Matt Cutts, Google 2006

The SEO starter guide describes much of what your SEO will do for you. Although you don't need to know this guide well yourself if you're hiring a professional to do the work for you, it is useful to be familiar with these techniques, so that you can be aware if an SEO wants to use a technique that is not recommended or, worse, strongly discouraged.