Separation from the world could be summed up in a pithy Puritan (though I forget the author off-hand) statement.
-- Dont do (or waste time doing) that which you wouldnt do on your last day, or what you would be ashamed to do in front of the Lord.--
For we dont know which day is our last, and the eyes of the Lord are always upon us. You may be embarrassed if the Lord was watching you waste your time trying to win a shiny bowling trophy; but at the same time feel no shame if you were spending time with your family teaching your young children how to bowl in the spirit of bonding. Many times it isnt "the thing" that is sinful, but the thing we make out of it. Titus 1:15 Take alcohol; it can be used to help with a stomach ache, or it can lead to drunkenness. Sex is beautiful in marriage, but detestable in whoredom. A kiss can be a greeting, but also a betrayal. Money can promote the Gospel, and can profane it. And the list goes on. The Bible not only explains the black and white, but how the grey is properly used. What examples of the saints were given to us? Did they spend their lives carousing, or focused on the life to come? God could have put any example of any saints in the Bible, yet what he has given is for our benefit. Where they fall, we can stand, and where they stand, we can mimic according to the measure that has been provided to each of us.