In the broadest category on the site, the only advice that applies to everything is also the most useful.
Decide what the thread is
A maker, a period, a subject, a format, a place. A collection is a group of things with a reason. Without one you have a cupboard, and a cupboard is hard to enjoy, hard to price and hard to sell.
The thread can change. Not having one is what costs money.
Where the first money should go
Several cheap examples of the same thing. Volume at the bottom of a category teaches you more than one piece at the top, and it costs less than the mistake you would have made on the expensive one.
The expensive beginner mistake
Buying the famous piece first. It is the most expensive, the most copied, the hardest to assess and the one you are least equipped to judge.
The second is accumulating: buying whatever is cheap until the collection has no shape.
How to learn without paying for it
- Read honest listings. Sellers who describe precisely are teaching you the vocabulary for free. Condition words.
- Ask what makes this one different from an ordinary one. The answer is the category's whole knowledge in one sentence. Questions to ask.
- Handle before you buy expensively.
- Record what you learn — what you paid, where it came from, what you were told.
Label everything
An unlabelled collectible loses most of its value the day you forget what it is. Write it down while you still know.
Store it from the start
Out of light, dry, nothing stacked under weight, away from an outside wall. Storing collectibles.
Questions people ask
How do I know what to collect?
Buy broadly and cheaply for a few months, then look at what you kept picking up.
Should I collect to invest?
Collect what you would be content to keep. The rest is speculation with storage costs.
When is a collection finished?
When you can say why each piece is in it.
More: buying collectibles, what one is worth.