Know the weight of what you're towing, and what the Towbar is rated to handle.
A lot of FWD cars, the towbar ends up with a rating which is only fractionally above the unloaded weight of your average homemade garden trailer
Though that limit goes up substantially when its braked.
To give you an idea, my Caldy's Towbar is rated 450kg unbraked / 1500kg braked - and I have a rear axel to bolt to
Engine power isn't the biggest worry - ultimately unless you have some uber steepness issues and/or your car will be heavily loaded whilst towing, most cars can handle a trailer borne load without hassle - but braking and general control are of concern. If the trailer has more than a certain amount of mass, jack-knifing under braking or cornering is a real risk. (My dad's 3SFE powered ST191 Corona was jack-knifed by a trailer load of dirt... not pleasant!)