As mentioned previously, Destiny 2 has two separate kinds of character progressions- an XP level, which is the more traditional kind of character level you are used to, and a Power Level, which is a composite average of the Attack and Defense ratings of your equipped gear.
Power Level has a soft level cap of 260- when you hit this, it is no longer possible for you to get it to go up in the ordinary way. However, you can still increase it to 300, which is the hard level cap. Just keep the following things in mind, to do once you have completed the campaign and hit the Level 20 cap:
- Unlock your Milestone activities, but don’t complete them yet
- Complete Lost Sectors, Public Events, and Adventures
- Start farming Planetary tokens
- Once you hit Light Level 260, start farming your Milestone activities
- Complete the Raid on Prestige- Completing it once on regular, and then again on Prestige, may actually be the only way to hit Power Level 300. So… good luck.