Build a habit of looking
Save works that stop you, even when they do not resemble one another. After a few weeks, look across the group for recurring scale, color, material, tension, humor, or subject.
That pattern is more useful than choosing a collection category in advance. It reflects your actual attention rather than an idea of what a collector should prefer.
Set boundaries that create freedom
Choose a comfortable total budget, then decide whether it is better used for one substantial piece or several smaller works. Include framing and delivery in that number.
Buy slowly enough to learn from each choice. Living with one original work often clarifies what you want next more effectively than another month of broad browsing.