I'm having trouble focusing.
- J'ai du mal à me concentrer.
You need to focus on your strengths.
- Il vous faut vous concentrer sur vos points forts.
You should concentrate on the road when you're driving.
- Tu devrais te concentrer sur la route quand tu conduis.
He is unable to concentrate on his academic work.
- Il est incapable de se concentrer sur son travail scolaire.