Iam very new to pcb design & i want to know, is there any rule for pcb layer stackup, like, is it necessary for a signal layers need an adjacent plane layer etc.
It again depends upon the controlled impedance of the board...Usually for 4 layer and above it will signal/gnd/vcc/signal,this stack up will reduce Emi and other issues......
You can get different stackups from the fabricators if your doin controlled impedance boards.