Did you really just ask this question? I'm surprised that such a basic question is being asked, did Google not provide an answer?
Anyway, to answer your question, the resistance of a wire (and a resistor made of resistive material, therefore) is directly proportional to the length of the wire and inversely proportional to the cross-sectional area. There's a formula for this:
R = p L
Where R is the resistance, "p" is rho, a resistivity constant, and L and A are length and area respectively. When laying out a resistor, you do not have control over the thickness of the resistive material (usually, but there might be some process out there...) but you do have control over the width - obviously Area = thickness X width so the area is directly proportional to the width.
The minimum length will depend on the process limits, and these are most likely to be set and enforced by the Process Design Kit, likewise the width will have a minimum as defined by the manufacturing process.
Hopefully this answers your question, if not, please read the hint in my first line of response.