First step is to determine if the MOSFET you are using is external biased or internal biased and if it is internal is it fully are semi biased. The biasing will be like this:
The BF998 and BF908 are external biased devices so they need gate and source dividers. The table establishes the values needed to bias the amp
The BF1105 and BF1109 are even less complicated since they are fully biased.
This data came from the Ap Note linked below. You can download it for more information.
Biasing Dual gate MOSFETs