just don't take it too seriously. simple is better than complicated in this situation. listen to the likes of finntroll and moonsorrow. they are just simple tunes.

take a basic minor scale and mess around with it until you get a melody you like. if you want to make things more original, you can simply add some ornaments: a pull off or a trill can liven up the most boring of tunes.

alternatively, you could consider finding a traditional folk melody and reworking it.

also, playing the melodies on an unusual (from a metal point of view) instrument can work wonders. try the melodes on traditional folk instruments (provided you have a keyboardist/synth player).

hope that helps.
My name is Danny. Call me that.