It is in the darkest of hours that the smallest light shines its brightest. - Me (Julie Michaud)
It is something that many have heard said differently, but it remains true. It is when the world seems the most bleak that we can acknowledge the tiniest form of good. When you know someone is having a bad day, week, month, or more, you don't need to do a grandiose gesture to cheer them up. Something as simple as buying them a coffee or tea, showing up to invite them out for a drive or walk, sending a handwritten letter to them, or sending them a movie night out coupon can be just the spark they need to remember that people do care about them.
Obviously this all depends on the person and your own financial situation. A parent cannot always drop everything and go for a drive. A patient cannot always have a coffee or go for a night out. There are so many little things that can brighten a person's outlook on life for you to choose from. Simply evaluate what you know would mean something to the person. Would a surprise bouquet of flowers, maybe their favorite species, help give them a reason to smile? Perhaps a half dozen cupcakes could perk their spirits.
What I do not recommend is what a lot of people tend to do. Do not belittle their strife. You may have had a similar experience, draw on that as a way to know how to help them, do not mock how they are reacting to it. Offer valid advice, not criticism. It may have taken a lot of courage to express how the person is feeling. Critiquing has it's place but not when trying to help someone out of the darkness. If you honestly cannot relate, don't. Just be there for them in any way you can. Do not use the phrase "I could never handle what you're going through", you mean well but that phrase is so infuriating to most (I bet they have heard it non-stop already), so try to keep that one under wraps.
Best phrase "how can I help you?" and mean it. If they say they need help piecing their life together, help them find the professional help they need. If they need one hour to themselves, help them figure a way to get that time. If they just need you to sit there and hear them bleed their heart out, get comfy and let them do it.
Be the light in the darkness. Be the hope in despair. Be the strength in their weakness. Be their friend in the void. Angels don't all have wings, most just have an open heart and kindness flowing from them.