There was an interesting thread here named
Did you make money domaining in 2019? and I was shocked to see many seasoned people here who said they made no money or broke even or even lost money this past year. I made about $3200 to $3600 profit, all on small sales. That is after renewals and new registrations. It took me a long time to learn what I should not do. Now my "should not" may be very different from other domainers, but I have learned to stick to it and I think it has helped me slowly start making money. I now know that if I build my portfolio next year, the percentages of sales and profits will likely follow the portfolio size.
Some of things I learned:
1) no more experimenting with other TLDs. I now stick with .COM. I may renew some of my other TLDs for a year or two more, but thats it. I do have success with pattern .org and some low priced .TV, but I dont like worrying about them.
2) stay away from trends. Sure, you see people making very nice money on canna, crypto, XR/VR, etc.. names, but there are many people here with hundreds of those names that don't sell.
3) no more chasing outbound unless I already own a name and realize there might be a buyer. I've done all the city, state, country outbound stuff and its very hit and miss. You see someone sell a name like detroitplumber.com for $500 and you think you can do it. You buy 50-100 nice GEO names and they dont sell or you only make enough to cover your costs.
4) dont buy "interesting" names that catch your eye unless you research them. Buy names that make sense and that you think could have a large base of buyers WORLDWIDE.
5) dont buy a name unless you HONESTLY believe you can sit on it for 3 years. If you don't think a name is worth renewing for at least 3 years, you might be breaking some of my rules above. You don't have to keep it for 3 years or more, but if you feel solidly about the name when you buy it, there is less of a chance you will hate it later on.
6) dont buy a name unless you HONESTLY believe you can sell it for $1000 USD. I dont mean you MUST price it that high, but dont buy a name you think might get you $xxx. Yes, you might sell it for $xxx, but if you genuinely researched it and really feel its worth at least $1000 then you are likely buying a name you will feel comfortable holding and not dropping after the first year.
Thats just a few of my rules. I know many of you probably will disagree with some, but we all have different goals. At the very least you must come up with reasons why you buy a name, why you price it and why you hold it. It cant just be random or you will end up with a portfolio of junk.