Having designed a fair amount of the DE units myself you can feel free to blame me for some of those choices. In the end I agreed to them all so even if they were Moscovian's idea that worked for me.

When I play them I almost always stick to 1+ initiative forces. The only thing allowed to have 2+ is aircraft since Slavebringers can't CAP. ^^

Here's a list I've used to great effect:

KABAL SYNDICATE [375]
6 Warriors, Ravager, Archon, 3 Raider, Sybarite
KABAL SYNDICATE [275]
6 Warriors, Ravager, Sybarite, 3 Raider
KABAL SYNDICATE [275]
6 Warriors, Ravager, 3 Raider, Sybarite
KABAL FLOTILLA [550] - Dracon is simply to make this BTS and not have 3 options for it.
Dracon, 4 Ravagers, Vessel of Pain
KABAL FLOTILLA [525]
Vessel of Pain, Sybarite, 4 Ravagers
KABAL FLOTILLA [525]
4 Ravagers, Vessel of Pain, Sybarite
BOMBER FORMATION [250]
2 Razorwing Bomber
BOMBER FORMATION [250]
2 Razorwing Bomber

With this crew my first order of business is to deal with enemy aircraft. If they have any that means CAP for one or both squadrons. For enemy artillery I just spread out as best I can and take cover. Most lists only have limited artillery so that works. If they have lots of it then someone is gonna have to make the mad dash up to kill it. They will die but that's life in the DE. ^^

I place my objectives as far apart as I can because speed won't be an issue no matter where I go. My deployment will be stretched out unless there is a drop army opponent in which case I will put my blitz in one corner and have nothing near it.

That's really key. These guys have 1+ initiative and speed 35cm. If they have to those Syndicates can lurk at the edges then on turn 3 they March and lend support. Always make full use of your Eldar shenanigans with the DE. They can do the normal movement and shooting tricks but they can also support assaults and grant crossfire when they march.

The Flotillas are the main force here. Their first job is to lower my opponent's activation count and then to take objectives. The Sybarite goes in the WE and the Ravagers hide behind that thing only coming out to shoot. If you avoid open spaces and the middle of the table you can normally position your Ravagers so they get cover from the Vessel. These guys are a surprisingly good assault force, especially if you attack vehicles. Remember a WE can use its FF value against units not in base contact even when based. So barge those 6+ CC enemies with it then shoot their friends!

Don't be afraid to stall against a slower army. If you can't move-shoot-move to get a target on turn 1 focus on hiding and being in a place that a mistake to chase you into. Then leap on anything that falls out of position. If the IG go on overwatch with their 45cm guns don't worry, you can probably find a place where only 3 of them can shoot you and either chew them down or let them shoot at 7+ against just your Vessel of Pain while the Ravager's hide.

Anything as fast as you are has to die first. Its ok to break it on turn 1 but on turn 2 try to finish them off. This is a good use for Razorwings once the aircraft threat is gone.

I also never worry about my own side of the table. If he wants my blitz or to go for take and hold he can have it. Everyone needs to be attacking on turns 1 and 2. On turn 3 I'll send something back to contest if I have to.

tldr; DE need to be cautious as well as aggressive. Look for an opening and then overwhelming force against the target.