Before anything, one must understand that good reputation is key to everything.
1. Once you have hurt someone, you cannot relent. You must destroy them, before they last long enough to return the favor.
2. Pre-emptive attacks can make the difference. If you have 30 health but they have 31, you must make the first move or you will suffer defeat.
3. You should avoid hurting anyone you've ever healed. Healing is a sign of alliance or truce, and breaking a truce is bad for your reputation and only encourages for others to attack you.
4. During wartime, it is critical your entire team focus on one person. Preferably their highest health person. By the time the war is over, that person will either be dead (offering less competition) or critically wounded (to later be finished off).
5. The cost of healing is hurting someone twice, so you have to be very economical and extremely aggressive from the beginning until the middle to ensure you are not eliminated early on. You should avoid dog-piles on the lowest HP of the bunch, and instead chisel away at high health people. By eliminating peoples' high health and giving them a normal health (15-24) you relatively make yourself a higher health and give yourself less competition / offer less provocation to enemies.
6. Generally, avoid offending others. Your goal is to survive first and foremost, not make off-topic comments.
7. As stated earlier, survival is the key. Understand that the ability to heal is not a blessing, but a curse. You must build a brick on one house but take 2 away from another, when you'd rather just take away bricks. You must take into consideration if you'd really like someone to have a lot of health later on, as in this game the heal tends to matter more than the hurt. (as you can win with as much health as you want, there being no limit).
8. Never allow yourself to become too extreme, low or high. At the perfect middle region, you do encourage people to try and get a quick kill, but it seems more people are drawn to the idea of tearing down a giant than fighting a mere Elf. Mediocrity is your advantage.
In conclusion, you must fall into the average, but you must not act average. Any misstep in doctrine can prove fatal for your reputation, your health and your team co-operation abilities.