Personally, I don’t think a Focus is a good vehicle for towing.
However, IF you decide you must do it, follow ALL guidelines in the owners manual and for the trailer. Do NOT overload the trailer, and maintain speeds BELOW the rated speed limit for the trailer.
Most of the trailers you find for rent at major chains have speed limits of 55 mph or LESS. U-Haul rates theirs at 45 mph. DO NOT exceed this speed under any circumstances - many trailers have a nasty tendency to wobble at higher speeds, particularly under the wrong load. That speed limit is there for your safety so that you don’t have an accident caused by the trailer going nuts on you, like in this video: