If your relationships are not a high priority in your life, let people know. Encourage honesty in others. Above all, be honest with yourself. This is the most important tool and sometimes the hardest to find. Spend quality time with yourself and find out what you're like.
Most people never do.
Learn to tell when you are moody or unreasonable or defensive or hyper-sensitive or blinded by New Relationship Energy. Know your limits. Discover where you could do better. Learn what's healthy for you and what's not. Figure out what your priorities really are.