Need dk 5v5 tips

[headbangeeeeerrrrr]

So, am l only supposed to use shadowbringer when l have dark arts?

You should be using shadowbringer more frequently, while keeping track of your health. Always try to line up your SB against multiple targets in a line for the most effectiveness. Just make sure to keep track of your health. Dark Arts is there to reward you for proper TBN usage.

Are There situations Where drain my own life is worth the risk? When l do get blood spiller, should l find a way to let enemy attack me first, so l can hit harder with it then recup?

The main goal of using consistent shadowbringer + bloodspiller combos is to be at low hp for the high risk = high damage playstyle. Proper use of such does involves a decent amount of macro.
Are you in a risk to get stunned/cc'd (whm, war)?
Are you in a risk to get focused + bursted (smn, sam)?
Do you have any of your defensives on standby (TBN, SE, guard/recoup)?

For any of these situations above, you should hold off from spamming shadowbringer and instead continue to 1-2-3 until there is a window for your burst.

Am l supposed to use salted earth to suck people off point? Or It should be primary used defensively to Soak damage on point?Qeuitus, should this always be combined with salted earth for maximum gain?

Salted Earth CAN be used to disposition enemies off the point yes, but also keep note of its defensive capabilities. Standing in that pool gives you 20% mit and 2k HoT. If you do not have SE available, consider playing safe unless you have guard/tbn up, before you engage another time. One example of a good SE usage is applying it to corner spots such as those in Volcanic and Clockwork. Essentially you're playing as a defender when a crystal sits at that particular spot.