Media Independent Handover (MIH) is a standard proposed by IEEE 802.21 working group to facilitate vertical handover support between heterogeneous networks. Currently, the implementation of the IEEE 802.21 standard supported in ns2, provided by National Institute of Standards and Technology (NIST) considers only the signal strength as a parameter to determine the destination network. Selecting a destination network using only RSS as indicator does not meet the needs of all users. For more accurate choice of destination network, vertical handoff decision should consider the values of different criteria of network as well mobile node. In this paper, we have proposed an improved handoff decision module including additional parameters which considers state of mobile node and network conditions during handoff decision in order to improve the performance. The simulation results shows that the proposed method achieves better performance in terms of throughput, handoff latency and packet drop over the basic handoff scheme. More over the proposed method helps to reduce the unnecessary handoffs by eliminating the ping-pong effect and thus increases overall system performance.