Hi Steemians, you should always follow this steps to get the most US Dollars (or any other fiat currency) from your Steem Dollars when you decide to cash out some of them. To get the most of your Steem Dollars, you should have an account on both Poloniex and Bittrex trading Platforms.
1.- Use Steem Prices (a contribution from fellow Steemian 
2.- This is the IMPORTANT step, wait till the gap between the internal market and the external market is reasonably small. I've find out that a gap of 5% is reasonable, waiting for it to get smaller would be really complicated. If the gap is more than 10% I would recommend you to wait, cause anything more than 10% is not normal, that means the gap should narrow soon.
3.- Once you see the gap is not too big, buy Steem with your Steem Dollars in the Internal Market.
4.- Send it to either Poloniex or Bittrex, the one with the higher Steem Price at the moment. Considering the prices in the image above as example, you would gain 2 cents per steem by sending it to Bittrex instead of Polonix, this is why I recommend having an account in both trading platforms.
5.- Sell your Steem for Bitcoin
Finally you need to sell the Bitcoin for US Dollars in any exchange platform that allows fiat withdrawals in your local currency. Remember that the smaller the gap between the internal market and the external market the more Bitcoin you will get, and more Bitcoin means more US Dollars.
I know this may be obvious for some of you but I hope some of you find it helpful.