A 3 step process from Pierre Finkelstein:
An excellent faux oak example from Vaughn Baker: https://www.youtube.com/channel/UCs1HEhysLI3nnuHoE8y6xDw
A fantastic woodgraining example from James Rowse who runs a Scenic Painters shortcourse at DAP Studios found here http://www.dapstudio.co.uk/about_us.html
These techniques could be used for a variety of wood types if the colours are adjusted, always have a good colour reference to hand.
For aged and distressed wood Vaughn Baker has a good example here, note his use of a sweeping broom to soften spatters: