A very common problem on the forward cast is to hit it early with power - you start right off hitting it hard. The term accelerate means to constantly increase in speed. The forward cast needs to start very smoothly and accelerate right to the final stop. You really need very little power on the forward cast - just smooth acceleration to a dead stop.
As mentioned previously if you start fast or hit from the top you cause the rod tip to bend immediately and if you slow down at all during the casting stroke it unbends some giving a tailing loop