Here's a few ideas off the top of my head:
Get involved with a player group. Working together to achieve a goal with other people makes the game a lot more fun.
Get into PvP. It's a whole different cup of tea compared to PvE, but it's a lot more interesting, challenging, and (personally) rewarding.
Try not grinding. Just pick a few missions that seem interesting and go do them. This helps to create variety in what you're doing, and even though it's not the best in terms of credits/hour, it feels less grindy.
Putz around in some signal sources. There's some new scenarios that came along with Horizons.
Get into Powerplay. I know a lot of people hate it, but if you get involved, follow the power subreddits, and hang out in their chats, there's actually a decent amount of strategy and large-scale teamwork that goes into being a successful power.
Go shoot some stuff in CQC for a while. CQC is really fun and well made, it just needs more players (and a better matchmaking system).
Role play as something. I know this sounds dumb, but, as an example, maybe you could pick a system and declare yourself the sheriff. Arbitrarily enforce whatever rules you like.
Go on a ganking spree. Become a minor celebrity as all the forum dads post endless threads with video evidence of what a sociopath you are for blowing up a video game space ship.
Try being a pirate. Pick a system with lots of trader traffic, and lie in wait. Interdict CMDRs (and NPCs too, I guess) and demand some cargo under threat of death. Make sure you're recording this so you can report all the combat loggers you're sure to encounter.
Mentor a nub. Find someone new and take them under your wing, show them the ropes, and help them make their first few millions.
Become a Fuel Rat. Every now and then you'll get assigned to go rescue a stranded, out of fuel CMDR, and everyone will love you.
Go participate in CGs. They're not always the best in terms of payout, but they're typically major hubs of player activity. Have fun, contribute to a larger goal, meet interesting new people, and then shoot them.
Buy an Orca. No, I'm not kidding. Pack it full of HRPs and surprise people with your porpoiseful love-touch.
If you're really that bored with it, I'd suggest just not playing until 2.1 releases. Loot, crafting, and an overhauled mission system are coming along with it, which should hopefully make things a bit more interesting. I'm especially hoping the new mission system is really good.