Technology of wireless sensor networks has grown thanks to technological developments in different areas related to microelectronics. However, to become truly ubiquitous, these networks must overcome a number of challenges such as resource constraints (energy, memory, etc.), quality of service (bounded transmission delays), etc. It follows that the energy conservation and latency minimization are critical functions for sensor networks. The ZigBee standard, combined with IEEE 802.15.4 offers the features that best meet the needs of wireless sensor networks. This standard defines the association procedure that allows the sensors to self-organize into a topology through which data can be routed to their destination. In this paper, we propose new approaches of association designed to optimize the topology formation of IEEE 802.15.4/ZigBee network. Then, we use simulation to validate their efficiency in terms of energy saving and optimization of latency for IEEE 802.15.4/ZigBee sensor networks.