Besides using off cuts to hammer them home you can just use a straight edge from a lenght of timber 2X1 or whatever, something small.
Some people recommend leaving the odd expansion gap even between the boards (essential to leave gaps at the sides, take off the skirting is best, or otherwise use that quadrant strips of timber you can buy to cover off the gap between the end of the board & the skirting.
Essential that the floor is fully dry before any type of timber goes down. I presume you and usuing polythene and/or foam underlay with it.
Tip, dont keep starting from the same side of the room, come to an edge and start going the other way from that edge. Size up any obstacles (door frames etc) and decide which side to start from, easier to cut a few bits off a full board to angle around a corner etc than to try to finish off with that tricky bit.
& obviously (but I've done it!) never cut off both the tongue & the groove from both ends of a "plank" as its then useless !!!!!