这是一个祈使句,中间嵌套一个定语从句.
其中,some of the techniques 是share的宾语,但是其后接一个定从（you have found ）,就比 with them 更长,所以就位于 with them 之后,实际应该是Share some of the techniques you have found to be useful with them .
to be useful是表达将设备分享后,能够使设备有用,但设备有用是发生在分享这个动作之后,所以用to do表将来.