Learn Turkish: Eskiden iyi bir okuyucuydum. - I was a good reader in the past.

It starts with the verb root oku (to read). We add the agentive suffix -(y)ucu to make the noun okuyucu (reader), using a buffer y because the root ends in a vowel. Finally, we add the past tense copula -(y)du and the 1st person singular ending -m to mean "I was a reader".

Is there a difference between okuyucu and okur? Both mean "reader".

They are largely interchangeable, but have a slight nuance. Okur (built with the aorist tense) often implies a habitual reader or an audience, like a newspaper's readership. Okuyucu (using our new -(y)ıcı suffix) focuses purely on the person performing the action. For a personal habit like "I was a good reader", okuyucu sounds very natural.

Why is it iyi bir okuyucu instead of bir iyi okuyucu?

In Turkish, the indefinite article bir must be placed directly before the noun it modifies, after any adjectives. So the structure is always Adjective + bir + Noun. Saying bir iyi okuyucu would sound unnatural to a native speaker.

Why does eskiden have the "from" suffix (-den) if it means "in the past"?