If you want stronger hips, strength training should be your first port of call. You shouldn't just focus on developing your hip flexor muscles though. You also want to strengthen stabilizers surrounding the hips like the hamstrings (thigh muscles), glutes (backside), and deep core muscles. Building comprehensive strength in this area will reduce your risk of injury.
The exercises above will target the hips, while other lower-body compound exercises like squats and glute bridges will also work this joint through a wide range of motion.
To increase your hip strength using these exercises, the usual strength training principles apply. That means you need to adhere to the progressive overload principle (gradually increasing the difficulty of these exercises) to see continued improvement.