You cannot tell someone that they are grieving wrong. Everyone has a right to deal with their pain in the way that they feel is best for them. It is very different for each person but that does not mean there is a right and a wrong way to deal with it.
You can be there for people. Offer your support in any which way you are able to. Some people are able to say the right things and others are better at making a cuppa. Some people give great hugs and a shoulder to cry on to those who need it. Others can come round and cook a meal. Some have the ability to make people smile. Some are great at just sitting next to others in silence. Do not force your help onto others, or force them into grieving the way which you yourself believe is healthy. Just show that you are there, if they need or want you.
Sometimes they might not even need you to be right there. Don't take this personally, don't get hurt. It isn't about you. Sometimes just knowing that there are people you can turn to is enough. One may not actually feel the need to turn to them.
Some people talk easily and others don't. Some people want to do as much as possible to take their mind off their grief. Others prefer to dwell in it.
Grief is not something that magically goes away one day. Perhaps the pain lessens for some but for some it's just learning to bare it on a day to day basis.