You can then take the brief - which should have sample colours, perhaps other logos they liked (not necessarily window tinting) and start sketching (by hand - it doesn't matter if you suck at drawing - like I do!)
Once you have a good range of sketches and ideas - pick the best 3.
And start producing them digitally on the computer.
Start off in black and white - then add colour as you go.
Stick to max 3 colours for a colour version.
And if you want - make an embellished version with effects and razamataz for their online presence.
Why not think differently? Rather than a logo that represents window tinting, how about a simple type treatment or visual style you can apply to different things that reflects this? Translucent business cards for example, or simple type that is darkened on one half. As a quick example I knocked this up for a friend to try out an idea:
Rather than a literal logo (a black cloud), the idea here is the name of the business looks partially obscured by a black cloud. This idea wouldn't transfer too well to print or other applications (and it's not 100% legible) but you could look at doing something simple with some type that gets the concept across much better than a logo.