All devotional expressions – be they japa, harinama sankirtana, preaching, studying, serving guru, cooking for Sri Krishna, or any seva should be done with enthusiasm. Enthusiasm and Joy is the key to bhava and prema.
Our coin of joy has 2 sides: One is Lord Shyama’s sweet glories. The other is the glories Of His sweet devotees.
Our happiness, our joy is simply to know that we are doing the will of Guru and Krishna, that's all. We don't need anything else.
If Krishna is pleased, you will feel pleased. This is automatic. If you are not feeling happy, that means Krishna is not happy by your service.
Spiritual life is not dry, it is also exceuted happily, 'susukham'. The result of that is not just happiness, but bliss, spiritual joy.