Tip #1: Don’t engage in the negativity: The first time you talk with a negative individual, provide a listening ear and offer help if needed. However, be sure to draw a line somewhere. If he/she goes into a negative swirl, let him/her continue, but don’t engage in the negativity.
Tip #2: Hang out in groups: Speaking to a negative person can be extremely draining so try have someone else around as well. Another plus point of having someone else around is that people bring out a different side to an individual. Thus, it may bring out a more positive side in the negative person.
Tip #3: Objectify the comments made: Negative people can be quite critical. They tend to drop insensitive comments that are hurtful, especially if they are directed at you. Rather than take his/her words personally, recognize that he/she is just offering a point of view. Sieve out the underlying message and see if there is anything you can learn from what he/she said.
Tip #4: Go with lighter topics: Some negative people are triggered by certain topics. If that happens, bring in a new topic to lighten the mood. Also, keep it to areas the person feels positive towards.
Tip #5: Watch the amount of time you spend with them: As Jim Rohn puts it – “You are the average of the 5 people you spend the most time with”. What this quote means is that who you spend your time with has an impact on the person you eventually become.
Tip #6: Identify areas you can make a positive change: Often negative people are negative because they lack love, positivity and warmth. Think about what’s bothering the person at the moment, and think about how you can help him/her in your own way. The key here is to be sincere in your desire to help, and to show him/her the upsides in life.
Tip #7: Drop them from your life: If all else fails, reduce contact with them or drop them from your life. Rather than spend your time with negative people, focus on the positive people instead. Remember that your life is yours to lead, and it’s up to you how you want it to be.
Source: http://zenhabits.net/negative/ (Abridged)