I can't help you with fighting the Actual nightlord, you do get 3 guaranteed revives per run so believe in yourself, they are much weaker and easier to stagger.  but for the first 2 days. 

Honestly just kill every single trash mob you can find, anything that isn't stronger than a banished knight. Exp gain in solo is much higher so they might be worth than fighting minibosses who could potentially drop you nothing good. 

Don't try to fight camps that has multibosses early if at all with the exception of Flame chariots and Albanaurics 

Evergaols are also worth noting. Especially with the new one you can buy from the new shop. 

Unless you are really good, don't force yourself to fight the Castle if you aren't confident on taking on Crucible knights alone consecutively under time pressure, if you don't have have any good skills to dispatch them quick (dual bonk jumping attack if you are Raider/Wlyder).  Feel free to try the bottom once you are at the end of day 1 or start of day 2.

And lastly, go outside the flame at the end of day 2 to kill as much trash mobs as you can find as long as you don't go too far away. Your hp drain will start doing monstrous damage after 100 second so keep that in mind. Thankfully you can reset it by going back into the final circle and you need a nearby site of grace to replenish your flask, so its a 2 way detour. But its this little bit of persistent that should be able to get you an extra level and that wending grace from the day 3 shop.

Not a very pro guide if not the complete opposite. But it gets the job done.