I have a level 152 full support druid and a level 144 dps druid on Epona. Sigils are an extremely useful tool, but for those of us who choose not to spend much real life money on the game for sigils alone, I'd like to offer some suggestions
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For background information, my 152 druid has probably 30 sigils and my 144 druid has none. I didn't use any sigils at all until I was level 120.
Certain skills have higher energy costs and durations. For example, at 20 points shield of bark costs more energy than abundance at 20 points. Shield of bark lasts 2 minutes and abundance lasts 3 minutes. With the strategy of extending my energy life, I have chosen to max abundance, and my shield of bark is only 6 points (5 from a bracelet). I love teaming with other druids in boss fights that specialize in bark, while I specialize in abundance.
Also, each cast of natures embrace costs as much energy as each cast of natures touch at the same level. Natures embrace only lasts for 45 seconds, so repeated casting is necessary. Again, with the strategy of extending my energy life, while maintaining effectiveness in healing, I keep my embrace at 17 points so it ticks just over 100 hp. This is sufficient for when I am solo druid in bosses and for helping dps members of a boss group who may get hit by area attacks/lava.
I make sure that my combination of skills I choose to specialize in compliment one another and present the most effective solution when healing. I change rings depending on the boss, or where I am training. I will be fair to say that after about 45 of intense training, my energy is low and I need to break.
Regarding my dps druid, she has max shield of bark, vines, lightning strike, and natures touch. She has a more difficult time with energy in boss fights, so she has 20 points in meditate to compensate. Unfortunately, she is only useful for 15 minutes casting those skills before she runs out and needs to meditate while casting only natures touch and shield of bark.
So, hopefully, this post will spark some ideas and people can begin thinking of ways to build their druids if they are having energy issues.
Take care, and have fun everyone!