If you're wanting to quickly get raid ready when Shadowkeep launches, or to simply hit the maximum power level of 960, there's a few key things that you can do. Firstly, and when the expansion pack goes live, all your gear will be increased to a power floor of 750.

• The soft cap is then increased to 900. After you reach 900, only Powerful and Pinnacle sources will increase your Power. 
• The powerful cap is 950. After you reach 950, only pinnacle (end-game) gear will increase your Power.
• The pinnacle cap is 960. Upon reaching 960, the only way to increase your Power will be leveling your Artifact.

As has always been the case, the sum of these numbers is based off your gear. However, Shadowkeep provides a Seasonal Artifact - similar to the Azerite Necklace in World of Warcraft - will give you power levels as you level up. The only downside to this, is that your Seasonal Artifact, and the subsequent power you receive from it, won't affect the drops you get. 

To power level quickly in Shadowkeep, you'll want to undertake the following: 

1. Pick the main character your want to raid on and reach 900 power (playing through Shadowkeep achieves this). Don't play powerful or pinncale content.

2. Swap to an alt, and repeat the process (by transferring a strong weapon to them). This then allows your "main" to begin gaining prime charges.

3. At 900 power on your alt, swap to your third alt and get this to 900 power also. 

4. Once you've done the above, and completed your powerful and pinnacle activities (on character number 3) you'll want to transfer all the gear you've obtained, to character number 2.

Crafting in the Mengaerie will still grant excellent gear, even in Shadowkeep. Use those Runes!

5. From here, hit up the Menagerie and forge gear. Items forged here is either at the highest power level you can get, or slightly below. You can then complete all the powerful and pinnacle activities on character number 2. Take those weapons you've gained, and move them to your main. 

6. Rinse and repeat this process, making use of item crafting (using runes in the Menagerie).