I have B1 visa for conferences. Due to some personal reasons I have never traveled to united states before. My B1 visa is still valid. Now, I want F1 visa. would this have effect to get F1 visa, since I haven't traveled with B1?
Yes you can, a friend of mine applied for F1 while holding a valid B1/B2 visa. His F1 was approved but they cancelled his B1/B2 visa.
Regarding not travelling to the US using the visa you issued, there is nothing official regarding this, it will be at the discretion of the interviewer.
Note: I hold two different types of visas now, B1/B2 and D, both are valid and I am using both.