IPEV guidelines overview
The International Private Equity and Venture Capital Valuation (IPEV) Guidelines set out recommendations, intended to represent current best practice, on the valuation of Private Capital Investments. The objectives of these Valuations Guidelines is to set out best practice where Private Capital Investments are reported at 'Fair Value' and hence to help investors in Private Capital Funds make better economic decisions.
Additional material: IPEV Guidelines Download
After this, you have a good baseline of what the best practices are and how are usually formulated