There are lots of things you could learn about light – but start by working out – where is the light coming from and how is it affecting your subject. Is the light coming from directly behind the subject? Sometimes this is unavoidable, and in those cases you can learn a few little tricks to make the light your friend. But as a general rule – if there’s a really bright light behind your subject – you’re at risk of a severely underexposed subject – aka, a silhouette. Sometimes this is great – but not if you’re trying to capture any amount of detail in your subject.
Natural lighting is always best – so try to keep that flash tucked away unless it’s absolutely necessary, and if you do need to use the flash – try to grab a diffuser – or even make one!