What are the best places for a lower-level melee fighter to train? I need to get my attack to 40 to wield my rune pickaxe.

Minotaurs are great at your level. Go to the room on the first floor of the Stronghold of Security under Barbarian Village and find the room south-east of the entrance with many level 27 Minotaurs. You can make decent profit off of their iron arrow drops, maybe 10-15k GP an hour and also great experience. Go to a crowded world with no people so they spawn fast. Good Luck.

Thanks for your help!

Yes, minotaurs are the way to go until, attack, strength and defence are all 40. There great, they can barly hit though 10 defence and full iron, they drop iron arrows like crazy and have an rare diamond drop, which comes up pretty offen.