Choose Niches that make money: People will buy a website domain if they think they can use it to make money. So buying popular phrases/words that could be associated with selling something like computers(.com) or hotels(.com) could be used by a company to sell computers or hotel reservations. However, something like Warof1812(.com) may not have the same business potential.
Whether you can use an existing backlink profile for a new web project under the available domain depends on whether the link target of incoming links can be reconstructed. In order to analyze which content was provided under a domain in the past, you can find out on the Internet Archive Backlinks have no value if they lead to nowhere and this can even have a negative impact. They are possibly redirected to similar subpages or homepages using 301 redirect. In this case the most part of the link’s power is lost.
Park the domain with a domain parking service. Since you may not have content to put on the site, a parking service puts up a dummy page with ads. When people visit and click on the ads, that's money for you. This method works best with popular keyword domains that get lots of traffic. In most cases, you will not have control over what ads appear on your domains.
The most popular place by far is ExpiredDomains.net. The main advantage of ExpiredDomains.net is that it aggregates data from a lot of different auctions and websites around the web. There are also paid services like DomCop. DomCom helps you identify worthy domains faster by displaying some additional data points that allow you to vet domains easily and in a unified interface. And finally, there are services that curate domains they believe are worthy such as JustDropped.com’s newsletter.
If you are looking to monetize an idle domain, looking to third-party platforms would be a good idea. Many of these platforms such as Nameforest ourselves will create a logo alongside your domain, which will be added to the list of preexisting domains on their sites. This is useful as the demand for your domain will also be greatly increased after it is rented as opposed to a domain that leads to a blank site - thus making it easier for you to find a potential buyer.
Check backlink profile: If you’re not familiar with what backlinks are, they’re basically any public website that “links” to the domain in question. Since there are numerous shady tactics in the SEO world, expired domains’ backlink profiles should be examined carefully. Check if too many links are coming from the same domain or if links have weird anchor texts/use foreign languages. You can use a tool such as ahrefs for these purposes.
Building a solid domain portfolio is not a piece of cake; it may take you several months or years to achieve this goal but it will definitely be worth it in the end. When you are in the fishing phase, look at the potential of the domain name. Another common strategy used by seasoned domain flippers is to get hold of some high profile domain names and sit on them until they soar in terms of value.
That said, my recommended budget for beginners would be $500+. Using this budget you could buy a bunch of high-potential $10 domain names, expired/dropped domain names or a mix of both. It’s very important to invest only what you can afford to lose and treat this as a side hustle till you get the momentum going. As you gain experience, industry expertise and some sales under your belt, you can then consider slowly growing your business into a full-time gig.