One big tip is to find a domain that someone can make money with. If you only owned that 1 domain, could you earn a living? This helps you focus on the top 1% of domains and ignore the junk that you will struggle to resell. You must get this right because domaining can bankrupt you fast if you buy the wrong domains. Godaddy is also great for grabbing expiring domains for much less.
Yes, buying existing domain names can be profitable too. Existing domains with a potential for profit can be found using Sedo. Make sure you pick domain names that have good traffic, backlinks and Google PageRank under 17 characters. Also, steer clear of existing domain names containing special characters or numbers because they are not likely to be sold.

I am really new to all this. I am about to launch my blog in the next week. I have a domain and a wordpress blog set ready to go. Clearly it will have no traffic from day one and I guess it will take a while to build up. So my question is would you advise a begginer like me to stick with the one blog for a while and build it up. Or is it worth investing the time early on to master how to find expired domains and link them to the blog?
While getting a new domain name will give your site a clean slate and allow you to start a fresh marketing campaign, you may not be aware of the fact that some expired domains come with a high Page Rank value. A company that buys such a domain will not have to work so hard on website promotion and backlink building techniques. Thanks for updating this really informative post!
Determine your domain's value. Before you start taking offers or listing your domain, take stock of its value so that you can come up with a good price. There are a lot factors to take into consideration when determining the value of a domain, so if you are unsure it may be wise to contact a company that performs these assessments. Some of the major factors include:
Don’t get me wrong, I’m not saying marketing your domain is not important. But, if you’ve bought a bad domain and you do (and overdo) everything laid out in this section and more, it’s still very unlikely that it would sell. It’s like spending car flipping and spending a huge amount of money, time and effort perfecting a car’s paint job, except that this car’s engine is completely fried. You’ll never be able to drive it anyway, no matter how awesome the paint job is, it’s irrelevant.

Thanks for this post. I do good with Adsense and wanted to branch out so I bought 5 domains from Namejet after reading this thread. After the 5 auctions ended I spent $500 total. I contacted 30 people about these domains and after a few bites I was able to sell one of them for $500 so I got my money back and now what I sell the other four for is all profit. The best part about this is that it is not very time consuming. I spent maybe an hour on Namejet. I spent maybe two hours sending out emails. Thanks again!
  Since starting SEO back in 2009, it has become very difficult to rank brand new domains. Unless you are building a brand, it's highly recommended that you start every new money site with an expired domain. Additionally, if you're building a PBN, you should only consider using expired domains. The problem is good domains start at $50 a piece, and anyone charging less is either full of sh*t or selling garbage domains, and I mean that. If it sounds too good to be true, it probably is. DomCop has a great offer that all of you buying expired domains should consider. For the price of a couple domain names, you can use DomCop for a month, snag some excellent domain names, which would otherwise cost you thousands of dollars. If you're considering expired domain software and don't have the knowledge to program your own crawler, I'd lean towards DomCop.   
There is NO accurate way to predict the sale of digital assets – if someone wants it, they’ll buy it. For example, those wasting their money on useless .com’s (LLLL’s that have no rhyme or reason) will spend 3x more time and money optimizing their useless name as someone that buys ANY keyword loaded domain (regardless if a TLD or new one). But these individuals who are spending thousands on domains will eventually get stuck with these domains in favor of (you guessed it) the oft forgotten yet highly useful 1-3 keyword domains. Why? Study Google’s algorithm as I have for over a decade, and you’ll figure it out.
The market-driven principles of the domain trade mean that a domain is only worth as much as the buyer is willing to pay. It is for this reason that criteria such as market potential and usability play such central roles in determining prices. Values can change at the drop of a hat. The price of a domain that was once of little interest to anyone in years past can skyrocket once, for example, a newly founded company takes interest in that same name.
You can easily find domains using the best metrics available from Ahrefs, Moz, Majestic, SEMRush, Similar Web, SEMrush, Domain Scope and Social Networks. We buy only the best, the latest, and, the most comprehensive industry wide metrics so you have the maximum amount of information to make a decision. No other tool gives you access to 90+ metrics.
It is mind boggling how local search engine optimization has grown from a tiny market to a mammoth industry within a span of ten years or so. This is also one of the reasons why focusing majorly on local names is profitable. From doctors to pizza parlors to salons, everyone wants to see their business thrive on the first page of Google Search results with the help of target keywords.

Also with the domains, a name which can be cheap for one can be worth gold for the other. Permute the letters in your domain name and try contacting and eventually selling out to organizations that run under those names or contain the letters within. Companies would be keenly interested in buying out the domain names that matches the product's name. Hint : Look for companies on LinkedIn

As people who normally use internet only to check emails, shop, tweet, upload pictures, update facebook status or conduct some business, a large majority of us remain oblivious to the domain name and domain flipping industry. So, when we do decide to venture into it for some reason, it is only natural for us to carry some commonly known myths associated with it. It can also be easier than building a website from a scratch. Although with easy to follow guides relating to how to create a blog – many are choosing to go down this route and add value to their domain names rather than selling undeveloped.

So how do you develop that instinct? NameBio maintains a database of over 500,000 historical domain sales (as of writing this post). They have interesting filtering features by which you can narrow down domains by price range, date sold, keywords and more. Simply sifting through the listings on NameBio long enough will quickly develop your domain appraisal “instinct”.