If you already have a character at level 50 and want to level some abilities or want to level an alt up these are my favorite methods to do so.
I really Don’t recommend power leveling for your first character i know a lot of people want to get to Champion Level 160 as fast as possible to get into the depths of the game.
Master Writs
While this is the most time efficient way to level it is also the most expensive one. Especially during a double xp event you can get a character up very fast with doing Alchemy and Enchanting Master Writs. Just power level eitehr of the skill lines (or both) to level 50 and then buy a lot of master writs. Then pre craft all of the needed items (on PC you can use Writ Worthy to mass craft them without effort). Then you just need to stand next to Rolis Hlaalu and use the master writ, hand it in, use, hand in, and so on till you are out of master writs. Every writ you hand in will give you 16840 XP (without double XP Event or Scroll).
Blackrose Prison
Requires Murkmire DLC
This is the second most efficient option if you know how to do it. You will need a somewhat geared solo build or know what you are doing to actually make this worth your time. You can do it on a low level character as well if you have enough self heals (a templar for example).
What you need to do here is: You enter normal Blackrose Prison and complete the first round in the first arena. In the second round you kill all mobs but the Elite Knight. Once you killed the 4 Archers that spawn along side him you wipe and keep repeating this round. To make this a little easier put Blood Altar on the back bar to get your HP down quick.
If you want to optimize this you go with 2 players one of you dies a little earlier and the other person uses the resseruction sigil before dying. The person leaves the res pending till both of you are dead and then resurrects. This will save you the time you usually wait for your resurrection.
Skyreach Catacombs
Requires 2 Players to farm
Skyreach is very similar to Blackrose Prison but with the advantage that you don’t need any DLCs for it. It is a little less efficient but easier and in the base game. The biggest disadvantage is that you need a second player in your group to reset the instance. This player can be offline so what works is ask in one of your guilds if someone is about to go offline or relog to another char. Tehy group up with you and then log off/relog to another character and you can reset the instance on your own. For this method we go in and start aggroing all mobs in the first room. Then we run right and go up the first stairs. We stop at the second stair case and kill everything there. Then we skip past the purple mobs (they have a ton of health so they are not worth it) and go into the next room. Kill all scattered mobs there and then start the Neidic chest event. After that is completed you run out of the room and aggro all add till you are next to the starting room again. Then you kill everything there.
Spellscar
Spellscar is an open world area in the middle of Craglorn just above Belkrath. It has a high mob density and requires no reset since the enemies just respawn. There are usually some people running around and you might be able to get into a group. To get easy xp you want to hit as many mobs as possible. I recommend wall of elements or the Arcanist beam for that.
Dolmens
The best space for Dolmen grinding is Alik’r Desert. All Dolmens are close to way shrines. If you put +dolmen into the zone chat you are very likely to get group invite which makes it even easier to receive xp and also gives you an opportunity to travel to your group members to unlock the way shrines. The three dolmens will rotate so you always wanna travel to the active one get some hits in and once completed go to the next one. There are usually tons of players around so you can just follow the train of players.
Training Setup
This is the set up i currently use for BRP farming. Is it the best solo CP Farm set up there is? Definitely not! But it does work well for me and was cheap to reconstruct (25 
per piece). heartland conquerer is highly recommended since it increases the weapon trait (training) by 100% and i like False God for the ease of sustain.
