Figure eight-knots are not directional. Once the knot is properly tied and dressed, it doesn't matter if you passed the rope through from the top or the bottom, it is purely a matter of preference.
Things to watch out for when tying your figure-eight:
- Does the rope go through both tie-in points, and not through the
belay loop? (like you mentioned in your comment)
- Is there enough tail, but not too much? (Your local gym might also require you to tie a backup knot)
- Is the knot properly dressed? (are there 10
parallel strands with no strands crossing each other)
- Is the knot properly tightened? (pull on opposite strands to tighten a
- Has the sheath of the rope-end you are tying in with not separated from the core, or has sheath-slippage occurred? (At the end of the rope you should be able to see both the inner core and the sheath, fused together by heat.)
- If your harness requires you to double-back at your buckles, are you double-backed?
- Some obvious ones: are you tying into the correct rope, is the rope and your harness in good condition, does your belayer know what he/she is doing, are you not crowding another climber, are you not in the fall zone of another climber...
There are climbing knots where directionality does matter. The clove hitch is the most common one; When tying a clove hitch, make sure the loaded strand is the one closest to the spine of the carabiner.