When properly held, the fountain pen nib should be upright so you can see the engraving on the nib.  Both tines at the tip of the pen should contact the paper at the same time.  Be sure not to apply pressure when writing, the weight of the pen is enough.  Most of us who are used to writing with ballpoint pens, have been trained to press down onto the paper with pressure when writing -- this is not necessary with fountain pens.
 
•FACT: The average right handed person writes with their pen at approximately a 55° angle to the paper.