Plants inside of terrariums are more sensitive to direct sunlight because they will quickly heat up inside a terrarium. Therefore it’s best not to keep them near windows in direct sunlight. If you have no choice to place them anywhere else because your room or office gets a lot of natural direct light then simply put up a book or some other object in front of the terrarium to provide a bit of shade. Generally terrariums thrive in non-direct to low level light. Some moss types that are commonly found in terrariums do particularly well even in very low levels of light.
No natural light?
If you’re in an office or room that doesn’t receive any light that’s fine. You can use a desk lamp or regular overhead light to provide a bit of light as needed. Just make sure that you don't put your terrarium too close to a bright light such as halogen light as it may cause excessive heat damage to the plants inside.
One sided growth
Plants naturally grow towards light as it serves as the primary energy source. If you notice that your plants are growing to one side, simply periodically rotate the terrarium to spread out the growth. If the plants are still growing in a haphazard way that doesn’t quite fit your liking you can always carefully manually reposition the plants inside using a pen or stick to nudge them in the desired direction.