Try

Act sooner rather than later
Being direct and honest; talking openly
Being positive; encouraging your friend
Listen carefully
Show empathy, be supportive
Taking care of yourself
Seeking help from a professional; telling a trusted adult
Be available
Be patient
Express concerns in specific terms
Feel confident that your friend can get better
Be aware and non-judgmental
Asking what you can do to help
Trust your instincts
Asking questions, be responsive
Educate yourself: Learn the warning signs
Pay attention
Take talk of suicide very seriously
Be natural, be yourself
Inviting your friend out for walks, activities and fun
Remind your friend there is hope

Avoid

Waiting to see if your friend feels better
Acting shocked
Being critical, skeptical or dismissive
Agreeing to keep secrets
Being patronizing or overpowering
Lecturing
Taking over your friend's life
Responding negatively
Avoiding the concern or issue
Judging your friend
Giving up or getting discouraged
Getting defensive or angry
Telling your friend to 'snap out of it'
Ignoring your friend's concerns
Suggesting you have all the answers
Being afraid of being wrong
Joking about the situation
Asking "why"
Overextending yourself
Trying to diagnose your friend
Managing the situation alone