Listed below are 7 golden rules:

1. Quality over Quantity
Domains are cheap so if you want to, you can hand register over 1,000 domains for less than $10,000. Would that make you happy? Would you consider yourself a "big shot domainer" if you were to own 1,000 domains? Wake up!
If you want to invest $10,000, buy a handful of domains which are actually worth it for 1 simple reasons: A domain with inherent value will always be in demand.

2. Stay Away from Over-Hyped Extensions
Do a bit of research and you'll understand why. Dot mobi domains are one of the best examples: people have initially paid a lot of money for them but as time went by, these domains started losing more and more value for one reason: the fundamentals just aren't there, dot mobi is an extension which has been over-hyped and nothing more.
The rule of thumb? .com is king. Register .com domain names for $8.41.

3. Avoid 4 Letter Dot Coms, 5 Letter Dot Coms etc.
Since the good domains were all taken, domainers started to register the remaining 4 letter dot coms, domains which are anything but pronounceable. Seriously, try it yourself: pronounce FYQV.com, now say it ten times and faster. Needless to say, as soon as renewal dates got closer and closer, people who owned awful 4 letter dot coms started becoming desperate. Some of the sold them in bulk for like a dollar or two per domain, some have simply let them expire and the same principle is valid when it comes to five letter domains.

4. Always Go with Reputable Registrars
Remember what happened with registerfly? If you want to avoid situations such as those, stick with registrar like IISP.HK which has proven itself very well.

5. Sell to End Users
You can buy lots of amazing domains on the cheap through domain name auctions and sell them for 10-20 times more to end users. This is a strategy which works for quite a few people.

6. Take Advantage of Type-In Traffic
Most decent domains have at least some type-in traffic, so don't just let them stand there and do nothing. Park your domains and if possible, make sure to also include a "this domain name is for sale" message on the parking page.

7. Develop A Strong Position to Negotiate
If you rely on domain sales in order to put food on the table, you'll never be in a great position to negotiate. Develop some websites at the beginning, offer some services online at the beginning or if you have a day job when you're just starting out, don't quit it just yet. A person who has to worry about paying off the mortgage and things like that is NOT in a good position to negotiate, be sure to keep that in mind.