How to... Open barred doors in the Soul Cairn
Within the Soul Cairn there are a number of areas that are inaccessible as the doors are barred, with no obvious switches or levers to open them. Think a bit more laterally though and you'll notice there are glowing orbs set in stones nearby. Shoot through these with either a bow or crossbow and the gate will open once all targets are hit, allowing you access to the hidden booty inside.
How to... Cure Vampirism
Being a bloodsucker is all well and good if you side with Vampire Lord Harkon, but it tends to be frowned upon if you're a member of the Vampire-hunting Dawnguard faction. If a Vampire attacks you there's a chance you'll become infected with Sanguinare Vampiris, which you then have three in-game days to cure by using a Potion of Cure Disease or activating any of the shrine blessings.
Should you end up going full Vampire, there's still a way back to normality. Speak to any barkeeper while affected by Vampirism and you'll be directed to a mage named Falion in the city of Morthal. After finding him and providing the item he asks for, he'll perform a curing ritual to rid you of any Vampiric tendencies, and this process can be repeated as many times as required.
How to... Access the new Werewolf powers
Vampires are not the only group to receive a makeover in Dawnguard, as Werewolves have also been overhauled. If you're already a Werewolf you'll lose that power by becoming a Vampire as you can't be both at once, but if you side with the Dawnguard or subsequently contract Lycanthropy then a new perk tree of Werewolf powers is available.
Like the Vampire Lord powers these perks are not unlocked by levelling up, but instead by feeding on the hearts of dead corpses, with a greater number of hearts required as more perks are gained. The new perks include greater strength, the ability to summon stronger allies and an additional health and stamina boost - which as a Werewolf unable to wear armour could make all the difference.
How to... Beat everyone at mounted combat
To coincide with the release of Dawnguard, the latest Skyrim update adds the ability to fight on horseback to your arsenal. Sadly you can't use magic in this situation so drive-by spellcasting is out, and bows/crossbows should only be employed for longer distance attacks as they are completely useless at close range.
Ideally, a long weapon such as a Warhammer or Battleaxe should be used for mounted combat as they can swing further and deal greater damage. Although this type of fighting can prove fiddly, it's useful as your horse will absorb some or all of the damage you would otherwise have taken... although you and your horse can still be killed so be wary against tougher foes.