Most people that get on a folding bicycle for the first time complain that the steering is squirrelly. Which means it responds unnaturally to turning forces. There are many ways to resolve this problem. The easiest solution is to install super small bar ends. Small bar ends will not interfere with the fold, so make sure to get the smallest you can find. Riders using bar ends naturally hold the handlebars further outside. This gives an angular force makes the bike turn like it's bigger wheeled cousins.
Now that we have bar ends we still need to set them properly for the rider, in the most comfortable way. Aggressive riders normally prefer them pointing downward, this will allow them to get into a tuck position Recreational riders normally prefer they point upward, to allow them to sit straight up. You may need to experiment to find the best spot for you, but this should give you a head start.
If you need more adjustment in the control area it would be best to use a high rise handlebar. A handlebar that has 1" or more of ride can be rotated around to create a longer or shorter top tube length. This will really allow the rider to stretch out and relax while riding.
So make sure you have small bar ends and a rise bar to dial in the comfort for your needs.