Software consultancy is a ridiculously competitive market; I don't want to scare you! but it's going to be tough.
The only reliable way to market and effectively present your company is to develop and advertise your USP (unique selling point), whatever it is.
I'm afraid it cannot be .NET development though; there are thousands of companies selling this expertise. However (I don't know the .NET environment) you can probably find niches inside the .NET market, for example you can advertise yourself as expert in the customisation of certain .NET-based products (lucene.net, umbraco f.i.).
As a general rule
- try to develop very specific skills (customisation of a product, adaption to a specific niche market, custom development of products for niche markets)
- advertise them as success stories
I know it might sound simplistic (and it is), but the point I hope to communicate is that it is important to focus on a few specific things instead of being a generic software shop. That doesn't mean you must not take generic development contracts if you can, but when you advertise and pitch your company it is important to make very clear what you do and why you are a better choice compared to the other thousand of cheaper competitors.