Choose clothing that blends with your brand - the feel, the look and aesthetic. If wearing a jacket, keep it fitted and think of a top/shirt underneath that will add a pop of colour. Primary colours (blue/yellow/red) work well as do jewel colours (jades/pinks/silver/gold).
What image do you want to showcase to clients - Is your brand modern, professional, creative, corporate, colourful? How can you translate this in your choice of clothing. Consider how your client will feel and react when they see your images online or in marketing materials.
Avoid clothing with busy patterns. Go for solid colours. Avoid plain black or white (where possible) as they can wash out skin tones. Large logos are a no-no as they are too distracting and don't date particularly well. Form fitted and tailored clothing is best.
Layers are good too so that you can mix it up quickly to give a totally different look.