There can be an expectation that revisiting a past life will be like being in a movie and while that is possible, it may be initially more vague than that but then become clearer with time and trance depth. Recalling past life memories is similar to memory recall in this lifetime. 
Memories can be triggered by the senses; for instance, the hot summer sun may trigger memories from holidays spent at the beach, the smell of apple pie may trigger the memory of Auntie Betty's home-made apple pie, the sight of an old friend may trigger memories from the past in which you both shared, a song you hear may remind you of a past romance.
 So when a person is regressed into a past life memory the moment the memory comes to mind it can be through the senses of taste, smell, sight, hearing, feeling or a combination of all of them.
Even though the past life memory may not be completely clear at first if the person relaxes into and goes with whatever arises it can become clearer as the senses are triggered. Just like when someone asks do you remember such and such and at first, it may be a vague memory but becomes more evident as the memory is triggered by little snippets of remembrance. 
As an example, a client doing past life regression could not see anything in her memory but could hear a sound which sounded like horses hoofs which then triggered her memory and then what was revealed is that she was sitting in a coach travelling along a cobblestone road.
Also what's important to note is that when a person is regressed that they are encouraged to observe the memory as if viewing a movie disassociated because some memories can be traumatic and by remaining disassociated they remain free of being overwhelmed. In saying that if the experience is positive an instruction to associate with the memory can be given. The benefits of associating with past life memories offer the opportunity to embody past life gifts and positive experiences and bring them as subconscious impressions back to this lifetime so that they can be acted upon and brought to life.