Lean on family and friends. They can be a great source of comfort during the loss of a parent, even if they've not experienced the loss of a parent themselves.
Forgive yourself for being human. Some of us have remarkably troubled relationships with our parents, and the loss of a parent may cause us immeasurable guilt, as there's no amending any past troubles.
Losing a mother or father is huge. It's not something anyone should just expect you to get over easily. These are people who loved us and raised us. They are the ones who know us best. They've seen us through the best and worst of our lives so far. So it's okay to grieve the loss of a parent. It's okay to not instantly get over it. Own your grief, because it's perfectly normal, and don't let anyone make you feel like it's not.
Now acceptance is a very misunderstood part of the grief process. Too often we think of it as being okay with the loss of a parent. It's not. Most of us are never okay with losing someone we love, but there is a point we realize that the person is never coming back and we need to move forward in our lives. We accept that the person is gone and we must go on living. Learning acceptance is, in itself, a process, because sometimes we feel guilty that we're moving on. Yet eventually we realize that life will never be the same again, but it is still a life that we can fill with joy and love. Most likely something our parents would want for us, even if they are not here with us.