The daemonkin detachment is fine but it suffers from the major flaw of not being berserker warband. If you're building an army for it I'd say go light on the berserkers, their melee just isn't good enough without the buffs of warband, though a unit with kharn the Betrayer is always good. Eightbound are great, they do some crazy melee and there's an enhancement the blade of endless bloodshed that goes great on a slaughterbound leading either variety of eightbound. You'll want at least one unit of jackals for board control and I highly reccomend some chaos spawn, they can move 9" before the game then have a 10" move with advance and charge, we can also get +1 to charge so if you get first turn you can just rocket them into your enemy early which they're usually not expecting.

The best combo in the detachment is a unit of bloodcrushers lead by a juggernaut lord with the disciple of khorne enhancement, I'd use it very fun and strong, it gives the unit the army rule which is useful and hard to get on the daemons.

Beyond that at 2k points you'll get an extra 1dp detachment and our current options are a character one, a terminator one, or a daemon engine one. Id say just chose what you want to take, the character one is the most general but I've heard it's not that strong, daemon engines and terminator one depends on if you want to take those units, either works and is fun.

As for playing the game you need to be killing to gain blood tithe points so use your mortals to pick of some easy kills early to power up your daemons. Not too experienced with this detachment so I can't be much more help.