One thing that I have found to be very important is: don't fight grief.
I've realized it's a normal feeling, you should let yourself feel it, it's only worse if you try to fight it.
Remembering "the good times" with common friends/relatives/??? instead of racking your brain with the "why" also seems to make it a bit better.
Other than that, only time will fix things.
Sorry for your loss.
I'll give the letters of seneca to Lucilius a glance.
Like another commenter said, don't fight it. The feeling will crop up at some very unexpected times, and reasons. There will be odd moments it returns when you thought you'd dealt with it. Only time will help. Even then it doesn't so much heal, but let you look back without the pain.
Losing my father young led me to make efforts to find out more about other relatives lives. Until he got sick I had, like many, just acted like he'd always be there.
I'm sorry to hear about your loss. I'm going to try to be closer to the rest of my family. Thank you for talking.
Take your time to actively process your feelings.
Leave your daily routine for some time and give your brain room to work undisturbed. Do something that keeps you physically active all day. Do something creative.
Explore your feelings and try to find out where exactly they come from. Don't give up just because thinking about it hurts more. It will help your brain to cope. Actively think about the countless positive memories you have. Bad emotions are much more powerful and tend to overshadow everything else.
Learn to accept.
Get plenty of sleep, it helps a lot.
Be strong.
GriefShare is interesting, they have a registry of meetups for those dealing with loss of a loved one > http://www.griefshare.org/findagroup
Condolences-
Realize that this part of you is with your friend as you had shared time, life and love together.
But in all that hurt and pain due to the loss also realize that there is a part of your friend still with you. Find it. Your tears will lead the way.
That might be a way love bridges even death.
Might take a dozen listens to internalize half the content, but it'd be adopting a different perspective on life. Won't come easy
I felt grief.
I started again but was infuriated.
Lesson: ALWAYS MAKE A COPY OF YOUR WORK!!
(You did not specify what kind of grief)