"Common intention" of several persons is to be inferred from their conduct, manner of doing the act and the attending circumstance. If one has intention to do any act and others share this intention their intention becomes common intention of them all, and if the act is done in furtherance of their common intention then all who participated in the act are equally liable for the result of the act. 

(13 BLC HCD 646) 

Common intention within the meaning of section 34 presupposes a prior concert. It requires a prearranged plan-a meeting of minds. 

(State Vs. Md. Shamim alias Shamim Sikder and others, 2000, 29 CLC (HCD) [4616]) 

The common purpose. Where persons joined together, moved by a common intention or an intention to do a certain act or cause a certain act or cause a certain effect for the doing or causing of which they have agreed or combined, and accomplish the common act, all are jointly and severally punished for the consequences even though all of them have not individually done the act or caused the effect; common intention implies a pre-arranged plan, an act, done in concert pursuant to that pre-arranged plan. Common intention as used in section 34 of the Code, implies a pre-arranged plan and an accused person cannot be convicted in respect of a criminal act by application of this section unless such act was done in concert pursuant to the pre-arranged plan. 

(Sarder Ali Vs. Crown, 9 DLR (FC) 7)

See, section 34 of the Penal Code, 1860 (XLV of 1860).