Water your plant (With nutrients or not)
High quality watering is very important to have healthy roots, and so a healthy plant. If possible, use rainwater.
Always wait for the soil to dry before watering. The frequency of watering depends on your specific conditions : size of pot, kind of substrate, type of lamp, ventilation, phase of culture...
A general idea would be that the plant needs ¼ of the size of the pot. If you grow in an 8 liters pot, you need to give 2 liters of water.
When watering, make sure to wet all the surface of the substrate. It is good to proceed in two times : a small amount of water to rehydrate the substrate, wait a few minutes, and then give the rest of the water.
When the substrate gets very dry it can compact itself, the water will drain directly on the side of the clod. To fix this, you can flatten the substrate with your finger and then give water very slowly.
After watering, you can confirm that the soil is actually wet by lifting the pot : it should be heavy.
When you need to water with nutrients, mix it well with the water and then proceed the same way you do with pure water. To be sure it's well mixed you can add the nutrients (liquid or powder) in the watering can before pouring water in it (and mix well with a wood stick). Follow carefully the instructions on the packaging and remember that if you put too much plants might suffer.
If you have decided to use powder nutrients (Guano, dry blood, seaweed...) you can mix it with the substrate when you repot, or mix it with your watering water or simply distribute it on the soil and gently mix it with the top 5cm layer of the substrate and then water.
Take in consideration that powder nutrients take time to be assimilated by the plant, so don't use it too late otherwise rinsing the substrate will be difficult.