Look one of the most important things you must have is determination to never give up and believe me there is going to be lots of time that you will want to give up.
That being said cheer up there also will be lots of time's that you will do great and feel like your on top of the world and can do this forever.
I remember some time ago when i still didn't know a nickel about buying and selling domains i was searching for expired domains and bought pornxpic.com and 2 other because they were in popular industries i put the 3 in auction has bundle on flippa but the title of the auction was just one domain didn't know how to change it to portfolio or bundle i was positive that it would sell and i really made a sale i think i sold them for 40$. A week or 2 passed and i learned about namebio did a search for pornxpic.com found out that it sold for 480$ in the past i got a little disappointed that i sold it for so cheap but at the same time got encouraged and thought that flipping domains was real easy so i bought another domain took a loss of 80$ lol just little proof that some times you just have to follow your intuition and have a bit of luck but never have over confidence.
From my experience you have to decide if you want to buy and sell domains has a hobby or has a profitable business. If you want to flip domains for a hobby you don't have any pressure you can have a job and invest in domains for the long run, if you want to become professional and profitable business in the domain industrie you have to spend all of your time living and breathing domains you also need big capital to play with real money. Has the old saying goes "If you want to make good money you have to spend good money".
The most basic and important steps you have to know are:
Never give up
In the domain world you need LOTS of patience.
Don't quite your job you also will need capital (maybe in the future when you have experience and good money from domaning you can go to your boss stick him the middle finger and quite if is a jerk of a boss xD if he was a good boss be polite and thank him for all the opportunities he gave you and tell him that you quite)
You need to do research and educate yourself even if you have 20 years in domaining you are always learning new things also the market changes every day and the more information the better.
Try to build your presence in the domain world the more people that you do business with that are satisfied and have positive feedback and good things to say about you doing business with them the more people it attract's because word gets around fast and they will feel more secure in doing business with you.
Always be polite and professional.
Never register trademark names and inform yourself about trademarks.
You need practice, knowledge and time to develop a intuition and understanding of what is a great domain and what it's worth.
Decide a strategy by trying many of them and see which one his best for you, example do you want to sell domains for cheap but fast, do you want to invest in the long term and wait for offers, do you want to do outbound sales etc..
Stay updated on coupons and subscribe to newsletters of informative domain website like domaining.com to keep updated
There are lots of areas inside the domain business focus on one example brandables, 4 letters, 1 word, IDN, new TLDs etc...
Try all the marketplaces and see which one is best for the type of domain your selling or buying.
Research all resources and tools like Namepros, Domainshearpa.com Dnjournal.com, Domaining.com, Namebio.com, Namejet.com, Estibot.com Efty.com Expireddomains.net, Domainsatate.com Dngeek.com and much more just educate yourself,
Other domainers also posted great advice and feedback in this thread follow there advice.
Hope this help's a bit.