Because I enjoy wakestyle I crash my kite almost every other tack and thus have gotten very good at relaunching kites. I find on 4 line kites the rocker techinque of pulling aggressively one way and then the other as the kite comes through the power zone to be most effective. Being aggressive yet patient is key.
One thing that has not been mentioned (much) is the importance of first fully depowering the kite before trying a relaunch in marginal winds. I was amazed the first time I did this as it gives at least a 20% advantage which can be critical. Using this with the opposing frontline technique mostly works for me, but there is always a lower limit proportional to skill and finesse.