Place everything where you want it to go. Don't worry about the cables yet. Assuming a small setup, place the main speakers to the left and right of the band, aimed slightly towards the center of the room. It is best to place them in an elevated position for the best sound projection.
Place one monitor speaker in the center of everything, facing the band. Monitors work well on the floor aimed up towards the players. The singer usually stands right in front of it, but you can aim it towards any player you want, or add more monitors as needed.
Put another monitor towards the back of the band for the drummer. This monitor will be for the drummer only.
Placement of the mixing board depends on who is running the sound for the show. If your band does its own sound, put the board where the band can reach it, but out of view of the audience. It is best, however to have the board and the sound guy out behind the audience.
Set up the microphone stands and microphones where you need them. Have one for each singer, one for each guitar, bass, and two for the drums if you have the resources. In a small club setting, you may not need microphones for the drums. Even with the loudest amplifiers, putting a mic on each instrument will allow you more control when it comes time to mix the sound.
Check the output jacks of your board and look for "Monitor." Using a speaker cable, connect the monitor output to a power amp, and the power amp to each monitor. Some more expensive systems give you control over each individual monitor, and some boards actually have an on board power amp for the monitors. Know your equipment.
Again using the speaker cables, connect the main outputs on the board (right and left) to another power amp, then to the main speakers.
Run XLR cables from each microphone to the board, assigning a channel to each one. Label them or remember which one is which, so you don't accidentally turn up the wrong one.
Turn all the main volumes down on the board and power amps, and turn everything on.
Adjust the volume levels, do a sound check, get down and boogie.