Photography print expectations 

-15 or more Poor under exposed

-10 below average under exposed

Good Exposure Full range from black to white

-10 below average over exposed

-15 or more Poor over exposed

If you left in developer the entire time you need more light (time or brighter setting) on the enlarger.
If you pulled the print out of the developer to soon you need lest light (time or brighter setting).

Developing is like cooking toast. 
Too light and it needs a hotter setting or more time.
Too dark and it needs a cooler setting or less time.

Too much light (time or brighter setting)

Up to -10 No whites or blacks Too much light in the enlarger and too little time in the developer.

Up to -10 Funny shapes = leaving your stacked up outside black bag and light got on it. Kind of a photogram.

Up to -10 Purplish tint means the fix chemical is bad aka exhausted or not enough time in the fix.

Up to -10 Dust and scratches on film or paper.

Up to -5 crooked in the easel

Weird lines of different developing= not dunking paper in developer the popper way

Focus...If neg is in focus use the grain focuser

Flipped negative. This is really bad if there is writing in the print.

Negative problems

good negative

Over exposed in camera. Use the light meter. Too much light.

Under exposed in camera. The numbers developed just fine print is light. Use light meter or get more light.

Not enough time in developer, or developer is cold, or bad developer notice the numbers are faded.

Spots on negative= not enough agitation

Streaks are caused by over agitation.

White fog on film is fix is bad aka exhausted or not enough time in the fix.