The ability to both convey and experience warmth and caring is critical to peoples' physical and emotional well-being, according to Kory Floyd in "Communicating Affection: Interpersonal Behavior and Social Context." Expressing appreciation and affection strengthens relationships and is often vital to productive human interaction. Not only does it feel good to the recipient, but the ability to successfully convey these feelings is rewarding as well.
Consider the recipient, the setting and the means of expression prior to conveying appreciation or affection. Unless your boss is an intimate partner, friend or family member, saying "I love you" is inappropriate. Similarly, you may be tempted to bestow your lover with a long, passionate kiss -- but should refrain from doing so in church or even in the post office. If you are unsure how to express gratitude and caring, do not do so until you have an opportunity to consider your options. Be pleasant and polite in the meantime.
Say "I love you" to friends and family and give compliments when they are warranted. Thank a loved one, colleague or neighbor and indicate why you are grateful. Explain the ways in which your recipient has impacted your life -- "I could not have passed this class without you as my tutor!" Provide support and encouragement by saying some version of "I knew you'd do a great job!" Spoken language is a direct medium for expressing thoughts and emotions, leaving minimal room for misunderstanding.
Hug or kiss, give a squeeze of the hand or a pat on the back. Touch is a primary means of nonverbal communication. It is intimate and immediate. Non-touch expressions are also imperative -- a smile with eye contact or a small gift are both effective tools for the expression of appreciation and affection. Sometimes just sharing quality time with someone is an adequate way to convey your regards.
Direct, in-person communication is optimal when expressing how you feel. However, not enough time or too much distance are certain barriers to success in this matter. Telephone conversations and email may be sufficient. The ever-rising popularity of social media can be employed also -- preferably in addition and in support of more intimate contact though. Use caution when communicating via these mediums; the lack of voice and body language creates space for mixed messaging.