I think this is a great question and contrary to many of these responses it is entirely feasible that you may need to explain these funds to either a regulatory body or law enforcement. Unfortunately, gov'ts tend to fear what they don't understand and that in turn means they will often act in ways they normally wouldn't in a more 'normal' situation.
I work in the industry in compliance it simply isn't true that the burden of proof is on the gov't. In the US if a financial institution reports on you AND if that reporting triggers action you very well may need to explain where these funds came from. And if you can't there may be some issues that go along with that. And folks must understand when it comes to anti money laundering and anti terrorism finance. Many governments are on the same page and their laws/rules mirror each other very closely.
To answer the OP- If you are getting the funds legally your best tool will be record keeping. Each transaction should be noted, with a description and if possible show a purpose i.e. January 26th 2013 market price of btc gained/lost X percent and my previous investment of XXX is now worth XXX. And of course you should have some register of how you came about those funds initially. As in Sept 3rd 2012 used $XXXX grandma gave me for my B'day to but X amount of bitcoin.
This way anyone asking can see a clear chain of your transaction history. If you are asking how to launder funds it wouldn't be proper for me to answer that or to tell you the best methods of laundering.