The best thing to do when using used coffee grounds for your plants is to mix it in compost and then use the compost to plant the plants.
But you can also just add the used coffee grounds to your plants and work them into the soil around the plants and then water the plants right after.
When you're adding used coffee grounds to your plants you should only need to add used coffee grounds once or twice per month to the soil around the plants.
If you put too much of the coffee grounds around the plants it can create too much acid in the soil which can harm the plants so only add the coffee grounds to your plants in moderation and no more than twice per month.