So I would've added a little simple 1 minute Lost Sector farm in here to quickly help anyone to get to 1200 power but thats just been patched late yesterday so its likely not going to drop as quick as it was before.
In all seriousness the levelling up to 1200, whatever you do will still be pretty fast imo. I reached around 1140 (start at 1050) after a solid first night hopping around on the new story missions and just picking up blues and a few purples everywhere. As the story missions become harder as you progress like @Baabcat says, its definitely worth popping around to do some other stuff.
Lost Sectors and Public Events are what i focused on between 1140-1200 because I dodn't want to lose the chance of getting a powerful gear drop too early from Crucible (Standard or Comp), Gambit or Strikes. If you actually do the Vanguard Strikes but just on a different burn to this week then you can get the rewards without triggering the Powerful reward off so this could be the way to go for you.
After 1200 the basics are Powerful Gear drops first if possible, followed by Pinnacle Gear drops. Also note that each level you go up in Crucible or Gambit will drop Powerful gear I believe - this is significant as you should be able to creep up slowly through the games.
Sometimes difficult to do because some powerful ones are get 8 bounties for Crucible, Gambit, Strikes which you'd have to do before you complete the number of matches it takes to get a Pinnacle but you can do it if you really focused on the bounty objectives.
As I first thought, levelling isn't a grind that should put you off this expansion. You will likely manage to get past 1200 before next week's Tuesday reset where you have access to all the Powerful and Pinnacle rewards again. Next week we will also have the Story mission and potential new PvE activity for this Season as what we've been playing on Europa so far is purely linked to the DLC. Getting to 1230 should be fine. I think its more how high an you get to do the raid after the contest mode has been deactivated which gives us all the best chance of completing the new raid.
Oh, DON'T FORGET!....GHOST MODS!
I'll try and put up a separate thread on it cos you really need to start focusing on mods now. They are making it easier to understand so it shouldn't be too difficult to see how to do it, however just for this particular levelling guide. Once you get to 1200, upgrade the energy on the Ghost so you can equip mods. You need at least 3 energy to use the mods linked to either Crucible, Gambit, Strikes & Nightfalls that will give you a good chance of dropping purple gear. Get used to changing this mod over and over (only costs 500 glimmer per change) so you can maximise the chances of legendary purple gear to constantly drop. I'm on 1212 with my artifact power included after 2 nights and i didn't do too much last night either. 🙂