Dexterity Ring
The Dexterity Ring increases your Dexterity by five points. Equipping the Dexterity Ring and Cale's Helm would bring your Dexterity to 13, more than enough to properly one-hand the Rapier. One-handing the Rapier is especially important during the fight against Freja because you want to hold the torch in your left hand to repel the spider minions.
Forest of Fallen Giants
Go to the locked door near the arena where you fought the Last Giant. Use the Iron Key to open the door. The area past the door can also be accessed by dropping down from above, near the Cardinal Tower bonfire, but you must equip the Silvercat Ring. Since you already have the Iron Key, you might as well access the area via a safe route.
Location of the Heavy Iron Key
Collect the Heavy Iron Key from within the area filled with Flame Salamanders. You need this key to access the Crown of the Old Iron King DLC. The Flame Salamanders are dangerous and should be killed with Poison Arrows. Use a Short Bow (or Long Bow) and snipe Poison Arrows at a Flame Salamander until it is poisoned. It might take up to a dozen Poison Arrows for the salamander to be poisoned, at which point use the Light Crossbow to snipe it with Heavy Bolts.
Iron Keep
Before fighting the Old Iron King, visit Melentia and purchase all Brightbugs from her if you haven't already done so. Start from the Eygil's Idol bonfire.
Old Iron King
This boss is weak against lightning. Buff your Mace+10 (or Rapier+10) with Gold Pine Resin. Note that the boss is weak against strike damage so it would take extra damage from your Mace than from the Rapier. At the moment you would most likely not be able to 2-hand the Rapier. Use your Mace+10 and equip the Peasant set (minus the Peasant Hat) to obtain up to 14 Adaptability. After entering the fog wall and triggering the cutscene, suicide your character. Doing so would trigger the boss to spawn at the left side of the arena once you enter the fog wall again, giving you plenty of room to evade his attacks. Bait the laser attack and run in to deal two or more hits. The fist slam is also a good opportunity to get in a few hits.
Defeat the Old Iron King to access Brume Tower. Chloanne now sells an unlimited number of Titanite Shards.
Brume Tower
Location of Dexterity Ring, Dark Souls 2: SotFS
Light the very first bonfire you encounter, i.e. the Throne Floor bonfire. Return to Majula and have at least 36,000 souls to purchase Brightbugs x 3 from Melentia. Warp back to the Throne Floor bonfire and grab Smelter Wedge x 6. Run past the first Ashen Idol that spawns, making your way to the nearby Dexterity Ring. Save the Smelter Wedges for later to deactivate the Ashen Idols in front of the arena of Fume Knight. Grab the Dexterity Ring. Equip the Dexterity Ring and Cale's Helm to allow you to one-hand the Rapier. One-handing the Rapier will be especially important during the fight against Freja.