I know I keep saying this over and over, but get yourself a good tripod aswell. A shotgun mic is very good at recording conversations or if your budget doesn't stretch to that, a couple of tie clip microphones will record the sound from conversations up close. You could also improvise a boom mic, using an ordinary dynamic mic plus cable wrapped around it, get someone to hold it above the actors heads and out of shot. This method is used a lot in television and film productions. Also record wildtrack to cover the sound of sirens or aeroplanes flying overhead which you can add in later at the editing stage. An editing technique used a lot in recording conversations is the use of Insert Edit, which I or whoever likes can post some info on using it.