Lighting is the single most effective change you can make to make your band appear more professional. Playing in the dark or under fluorescent lights or the pub's normal atmospheric wall lights looks rubbish and makes you play badly ….
If you are playing pubs or small halls you can get away with something like 4 or 6 of the small “4 bulb” light boxes from Maplins (usually about £20 each) or a pair of those and a pair of the Maplins “Disco Light Bar” stands (4 lights on a T bar stand) Have a look on the Maplins website under Disco Lighting. A total spend of about £120 shoud do it. The extra gigs you get offered will pay for the gear in no time.
Where should you position them? - One on each PA speaker top, facing the band's front person - One on each side of the stage at floor level shining inwards - Two shining up the back wall behind the drummer or backline (make sure you don't fry any cables or you drummers @rs3 though..)
You need to shine light on the face of the band's front person as a minimum. As most of us use PA speakers on stands, the tops of these are a good place to put your light boxes, facing the stage, angled in. Some PA speakers have threaded bolt sockets on top for when they are hung from cables in Theatres etc. Use these if you can, otherwise some strong luggage straps (cheap from IKEA) will hold the boxes in place. Be careful of the heat the bulbs create and position your straps accordingly.
For best effect, run all of the light power leads from one power switch so that they can all be turned on and off in one fell swoop. This then givs you the possibility of a dramatic switch on once you are on stage ready to start playing. It also lets you switch all lights off atthe end of yoru set like they do in big concerts ….
Add a Maplins mirror ball (£5!) and a couple of cheap rope lights for cheesy gig (try Lidl/Aldi at Christmas :) )
More professional rigs can be bought as packages or built from components depending on your level of competence. Most commen are PAR (Parabolic Aluminized Reflector)cans mounted on T-bars (stands with a bar across the top - looks like a T). These come with a lighing controller and can be built into very sophisticated rigs with mixtures of floods and spots.
A recent development has been the iColour units with 3 or 4 lights built into each unit. These are often sold as packages with cases for the light units that offer more protection.
More recent still packages with LED par cans have started to appear on the market. These have the added advantage of not giving off lots of heat and can be considered environmentally friendly as they have a very low power consumption.
A google search for “band lighting” or “icolour” will bring up the best deals.