Be a Catholic
It is important that you should be a Catholic to become a saint. This is also important you are baptised in a Catholic church.
Sainthood is not something that you could get during your lifetime. It bestowed upon someone who lived a virtuous life and dies a good death as it also inspires people. The Church authorities look into her or his life and then decide whether sainthood should be bestowed upon some particular individual or not.
It is important as some devotional group follows you and your good deeds. Sometimes it is not intentional that a number of people are following you and your good deeds but it is usually unusual that when you are doing things in right manner, a few people witness it and appreciate what you are doing. This process slowly grows and at a certain stage, you have quite a few individuals who are willing to call your deeds virtuous.
Investigation into life
When you die, your life will be investigated as to how holy you lived your life. This will take some time as the Catholic Church as its own way of investigation to look into someones life.
Local church authorities send the case to Vatican
Another interesting point is that after your death, the local Catholic church or local bishop sends case to Vatican and then the Pope will decide whether sainthood should be given to someone or not. This is also a lengthy process and takes many weeks to finalise any name.