There are several stages to keep memory in human’s brain. In the other words, it is divided into three steps as the process of memory, from sensory to short-term to long-term memory. Sensory memory is the shortest memory in the brain. It received information through five senses of sight, hearing, smell, taste, and touch, which last 1-3 seconds but retain accurately. For instance, people saw something and remembered what it looked like is an ability of sensory memory. Short-term memory (“working memory, which is essential for human cognition, can be thought of as a mental workspace or the brain’s notepad- a neural system for storing and manipulating small amounts of useful information.”) last 15-30 seconds and it is closely related to the process of sensory memory. If people receive new information without repeat old information, the new one will push out all information from brain. “Short-term memories can become long-term memory through the process of consolidation, involving rehearsal and meaningful association.” But when people rehearse information, it turns to long-term memory. Without rehearsal, the information is lost from the short-term memory and forgotten. Long-term memory is obviously stored information for a long period of time.
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Types of Human Memory: Diagram by Luke Mastin

It is necessary to improve memory in different methods. People’s lifestyle is a based way to keep memory. Firstly, the food what we eat play a crucial role in human’s memory. “Fresh vegetables are essential, as are healthy fats and avoiding sugar and grain carbohydrates.”(Dr. Mercola, April 24, 2014) In addition, exercise encourages our brain to work more quickly. Regular exercise can help us avoid the memory loss that comes with aging. Exercise also makes us more relaxed, and can also improve our memory uptake, allowing us to take better mental "pictures". What’s more, sleeping enhances the brain's ability to control behavior and memory. Getting a good night's sleep (a minimum of seven hours a night) may improve our short-term memory and long-term memory. The link between sleep and memory has a long history. “The Roman rhetorician Quintilius noted, in the first century AD, that a good night’s sleep enhance memories, and early research into the phenomenon was published in the mid-1920s.The past decade has also seen a growing body of evidence which clearly shows that sleep plays an important role in the consolidation of newly formed memories.”

Memory is an important part in our brain with different influences in human’s whole life. To start with, people in different ages have different memory ability. As a child, memory is a learning ability to remember something what they see or what they like. When they grow up to be a teenager, memory is knowledge what they have to learn or accept. When people are adults, memory is a life experience what is experienced by them. As an old man, memory is a recalling what likes a film in their whole life. Secondly, practice is one of significant influence to memory. However, different kinds of people have various opinions or ways to practice in order to keep or improve memory. For example, children and teenagers are easier to remember things than old man. So old man should spend more time and energy to remember things than young man. But it not means younger is best advantages for memory. Someone who is veteran is better than children or teenagers to keep something because they get some great methods to keep memory for their trying different practice. Finally, accident is another reason for people’s memory ability. For instance, someone who is scared by some horrific things what they can’t accept by their brain may forget that by election from their thinking.

Losing memory is common things in human’s life in various situations. On one hand, people loss memory with their growing ages. In the other word, they may not store information as the same in different ages because they couldn’t stay in the same situation all the time. “Hormones and proteins that protect and repair brain cells and stimulate neural growth also decline with age.” For instance, “Older person often experience decreased blood flow to the brain, which can impair memory and lead to changes in cognitive skills. Older people are less efficient at absorbing brain-enhancing nutrients.” As we all know, people meet different friends or neighbors in their life. On the other hand, disease is a fatal problem for loss memory. For example, someone who gets AD Alzheimer’s Diseases may not remember what they have done or who is him or her, something like that. Eventually, people choosing something they don’t want remember or recall forgets it, such as horrific sight, embarrass time, or bad result of some important things.
References: http://www.helpguide.org/articles/memory/age-related-memory-loss.htm#aging http://www.human-memory.net/types_long.html http://articles.mercola.com/sites/articles/archive/2014/04/24/memory-improvement-tricks.asp
The human brain 50 ideas page 89, 93, 101
http://www.simplypsychology.org/short-term-memory.html