Finalize the script and create a script breakdown. Make a storyboard if possible so that it's much easier to do multi-tasking work without missing out in any big or small detail. The script breakdown also makes it convenient for you to have an accurate checklist of all props, sets, actors and schedules you need during the shoot.
Divide the tasks between the four people in the production. For instance, the director may also act as the cinematographer, then the production designer may also be the wardrobe person, hair stylist and make-up artist. Meanwhile, the producer may also be the sound recordist, while the assistant director may also be the script continuity supervisor and crowd control person. At the same time, these people must also consider being open to other tasks as location managers, production assistants and runners. The director may also work as the editor and animator come post-production time.
Prepare all art requirements ahead of time. Do these preparations in between production meetings and during the times you fix the schedules of the actors, locations and prop, set and additional equipment rentals. This also allows you to update the needs of the production and make the necessary changes and adjustments before the actual shooting day.
Go mobile with your choice of technical requirements. This is the most practical way for the on-the-go and guerilla-style filmmakers who need to multi-task. Choose small, easy to carry lights, reflectors, gels and diffusers. Since setting up every scene takes a while, using a portable camera where the crew and actors can easily move around and transfer from one location to another faster is the best way to go.
Follow the shooting schedule, script breakdown, shot list and storyboard during the shoot. However, be open to unexpected changes due to uncontrollable situations that may happen along the way. If you prepared for various possibilities early on during pre-production, your four-man crew can handle the pressure and the challenge of multi-tasking and troubleshooting during the film shoot.