Ok, well welcome to the Dark side!
My first suggestion would be to read Kei-Ariq's post on Army List Advice which can be found as the first topic in this forum (or as a link in his signature). It has a lot of useful advice on starting an army. But before that I will offer some advice of my own.
1. Speed is the DE players greatest ally. So the more Raiders you have in your army, the better off you are. If you can, mount everyone in some kind of vehicle.
If your're going to take Sniper squads I would suggest that you take two for the fire support. Let the rest of your troops get into position quickly on their Raiders.
And those Raiders should have DL's for dealing with enemy armor.
2. Ravagers (although not exclusively) are best used as anti-infantry. So mount them with 3 Dissie's and watch the enemy troops die by the score.
Give them the Night Shield and screen them with your Raiders until they are in the position to deal the most damage.
3. An Archon or Dracon with Incubi in a Raider is a solid HQ choice. Just don't go overboard on the number of Incubi that you take. No more than 5 or 6. Otherwise the unit is over-piriced and will take away points that could be better used in other units. (and with only 5 or 6 the unit is still highly effective in CC)
You also might want to consider putting your HQ on a Reaver or on a Skyboard. It can really help make them CC monsters and allows you some diversity in your army and tactics.
4. You can't have any more than 3 squads of Wyches in a Kabal. If you're going to take them, give them Raiders. Running them across the board will get them nothing more than shot up before you need them.
I normally take only 1 or 2 squads of them in my Kabal. The have always done the job very effectively for me with those types of numbers.
5. One other unit you might want to consider. Reaver Jet Bikes. Three reasons. a. Mobility and speed. b. Great tank Hunters with Blasters mounted on the bikes. c.In a pintch they are great for addition assault support or can be used to assault on their own.
Those are just some basic suggestions. Once you have your core army you can tinker with it until it suites your play style.