The following are some bare minimum requirements for the setting up and running a mail order book business:
If you have more than 6 books you need a plan to keep your inventory organized, and you need to be consistent in using that plan. Every dealer has had the situation where a book has sold and then could not be found, trust me there will be a certain point where your inventory will be too large to trust to your memory.
How you store your books is your choice, but they need to be in a dry, cool and clean place if you want them to be in the same condition when you ship them as they were when you described them. Also beware of sunny windows, they will fade dustjackets and even books spines with time, some colors (yellow and blue in my experience) will fade even more quickly.
Invest in the Zempel reference book on how to distinguish a first edition. The small McBride pocket guide is also very handy for book scouting but unfortunately is currently out of print.
Take some time to become familiar with the traditional bookselling terminology, you may never use them in your descriptions, but you really should be familiar with the terms.
Beware of creep or slip in your condition descriptions. When processing a stack of books it is very easy to start describing the condition of the books relative to each other instead of relative to the standard of Fine in a Fine dustjacket.