Often the power of parties within a legislature is considered in terms of whether they can win votes on the floor of a House. Cox and McCubbins point out [Setting the Agenda: Responsible Party Government in the US House of Representatives - New York: Cambridge University Press, 2005] that the real power is to set the agenda - to decide which bills are voted on at all.
In Congress there are a number of blocking actions open to the majority. A Chair of a committee may delay or decline to schedule hearings; the Rules Committee may refuse to report a special rule - allowing the bill to be torn apart should it be considered on the floor; or the Speaker may delay the bill. In the House of Commons the Government controls the overwhelming majority of time. Private Members Bills considered on Fridays can be "talked out" by members acting on the government's behalf.