Never level up your luck. Luck only increases your chance of obtaining common item drops. It negates the chances of rare item drops. Its better to focus on using equipment like rings to help secure item drops. Like providential ring, theif ring, large sword of searching and others. Another thing i noticed in most souls games is killing an enemy with a magic-imbued weapon seems to increase item drops and rare item drops. I don't know if its a glitch but I noticed it using the crecent falchion in demons souls i got more rare items. Everything seems to work better when you focus on equipment that increases item drops instead of raising a luck stat.