Loneliness and Dispair
These two devils go hand-in-hand and are unlikely to be too far away during bereavement. And, the closer the person who died was to you, the more you will need to be on your guard.
As a bereaved person, it would be a mistake to attempt to make your life so full and busy that loneliness cannot enter. Indeed should you succeed in such an attempt it would only be to delay the inevitable. I think it is more useful to anticipate the feelings that will be experienced at times of being alone, to acknowledge that life is now different but importantly to have something to aim for: a light at the end of the tunnel.
A diary is a useful tool for efficient planning of life. Perhaps before bereavement, a day could easily pass with nothing more exciting than the television to watch, but this may not work now. Planning some days in advance with a little something each day that will just take the edge off an otherwise empty day, can make all the difference. Perhaps it will be a trip to the shops, a walk around the park, a bus trip out into the country and back.
Loneliness is closely associated to boredom and in turn boredom is closely associated with depression; potentially this is a slippery slope. It is almost inevitable there will be moments of both but if they are anticipated and controlled with something more positive around the corner to consider, then you can avoid despair setting in.