I use a high timeframe to look for strong trends- for example a 4hour or 8 hour frame may show that a particular pair has been trending down for a few weeks.
I then look at a lower time frame, 1 hour, to confirm this is still the case and that my pair has not started to change direction.
Finally I look at a lower time frame, 5 mins, to pinpoint my trade entry point.
The point at which you close a trade will depend on your trading style and strategy. Are you trading short or long term? Do you want out before upcoming high-impact news? How many other trades are open and what degree of risk will you take?