It really depends on how much time you have to invest. On the low effort end, you can put some money into coinbase and speculate that way. On the high effort side, you could mine the "up and coming" alt coins on a box.

Personally, I'm telling a lot of my friends to put a few hundred bucks (money they won't mind losing) into coinbase and evaluate afterwards. At the least, it's an interesting tech/story so having some money involved makes it fun. There's also speculative upside, though idk if we're past the "easy money" stage or not.

I still think "investing" in bitcoin is a gamble and I'm not convinced it should have a place in your portfolio. Not only because of the speculative risk, but the added risks of forks, hacks, etc. I'm really concerned about how liquid the market is and should an event happen, the little liquidity that exists will dry up.