Written by MSG Commander
Before continuing with the story, I highly recommend that you do all of the following:
Strengthen everyone's armor to +3. (This should already be done, but if for some reason you haven't done it, do it now.)
Before you can upgrade some of these weapons, you'll need to have all the treasures up to this point, including from Earthdepths Lake (depths) and Dust Hill (underground).
Strengthen Kline's weapon to Ice Sword +4. (You can trade Large Iron Ore for Silver with the witch in Vaneisha Village, but you can't get Silver Chunk yet, which you will need for Ice Sword +5.)
Strengthen Alia's weapon to Lancer +2. (That's as high as you can go until you can get Magic Beast's Claw.)
Strengthen Paola's weapon to Vigorous Blossom Flower +3. (Again, you can't go any higher until you can get Magic Beast's Claw.)
Strengthen Fred's weapon to Snake's Poison Fang +5. (You can choose any of Fred's swords, but I recommend this one mostly because I like poison, but also because it's much easier to collect Purple Bat Fangs than any of the items you need for the other swords.)
Additionally, you should go to a Weapon Shop and buy 1 Long Sword, 1 Battle Whip, 1 White Double-edged Sword, and 1 Bewitched Cicada Flower. You're about to get another Crafting Recipe which will allow you to start strengthening Level Two weapons (but the weapons you currently have will still be much stronger for a good long time).
Complete as many witch's requests from Ensen Hamlet and Vaneisha Village as you possibly can.
(You'll need to go through Dust Hill (underground) to complete the request for collecting Torrent Branch.)
Be sure to steal Purple Bat Fang from every Giant Bat you encounter in Earthdepths Lake! (You'll need it for Fred's weapon.)
Also, any time you run into a Gelatin or a Magma, steal Gelatin Ball from them (you'll need it to strengthen a weapon you get much later).
Challenge the Gatekeepers in Earthdepths Lake and Dust Hill, and get the treasures in the depths.
You should be able to handle Earthdepths Lake (depths) and Dust Hill (underground) if you max out everyone's equipment and level up to about 28 or so. If not, then just get the treasure and get out - you'll be coming back to these two locations for later witch's requests anyway.
Skip the Gatekeeper in Elyups Cave for now. (You're not nearly strong enough to survive his attacks yet.)