Feelings can be easy to hurt and hard to mend. So if you care about someone you should try as much as possible to think of their feelings when you do something or you are talking to them.
Everyone has heard the old adage about catching more flies with honey than with vinegar. Here's a spin on that: usually you can get get further with someone by praising and appreciating what you see in them that pleases you than you can by running down or criticizing what doesn't please you.
Try to be negative in your speech as little as possible. This way, when a situation arises where you have little choice than to express something negative, they are more likely to be willing to accept it because they know you do value many things about them. Even when being negative, there is seldom a need to be harsh about it. Do it as considerately as possible.
Do they have a hobby or activity you see no point in or find boring? Even if you don't join them in it, you can be happy for them, compliment their efforts, celebrate their successes.
Do they sometimes wear themselves out doing for work, or home or school or others? Don't nag. Instead look for a way to ease their load, even if it is only a small thing.
Is someone trying to apologize to you or explain some error they made to you? Don't cut them off, let them finish. Really listen. Chances are when you do, you'll actually feel better toward them. And even if you don't, they'll at least no you heard them out.
Bottom line is, if a friend, parent, sibling, spouse, co-worker...anyone, is of value to you, then value them by your actions and words! And here too, pray and ask God to help you see them as He sees them. To show you how to be to them what they need you to be. What He would have you to be to them, with them and for them. Respect them, applaud them, cheer them, cry with them, comfort and console them. Are you happy to see them? Let them feel it! Miss them when they are gone? Then show it, express it.
This world tears us down in some way every single day. We each need a place, a person, in it to mend us, strengthen us, support us. And life is short. Life is fragile. When it comes to expressing your love, friendship, etc...there is no tomorrow. There is only today, there is only now.