If you are a day trader then I suggest closing your trades by 12pm EST (U.S.) on Friday’s since after that usually the market comes to a crawl.
If you are a swing trader then check the trend on the daily chart. If you are in a position trading with the trend and if you are in the positive by 50 pips or more then I would suggest you leave the trade open. I would not open a new position or add to one on a Friday.
There is a risk that the market may gap against you on Monday. Although I have observed that the gap is almost always in the direction of the daily trend. I usually take my stop loss order off before the close of market on Fridays so if a gap occurs against me then I have the opportunity to mitigate my losses. This is a risky move and I don’t recommend you do this unless you are well versed with market analysis.