How do I fertilize my plants properly?

Potted plants don't need fertilizer for just a few weeks after transplanting.
And then, the timing of fertilizing and the dosage are selected individually, depending on the growing phase and time of year.

7 rules for fertilizing:

Time to apply fertilizer.Actively begin to apply fertilizer at a time when the plant begins active growth. This time usually begins in March and ends in September. However, since every plant is different, it is advisable to check the time of application specifically for your plant.
First things first, you need to follow the instruction that are indicated on the packaging. But usually fertilization is considered to be once every 2-3 weeks. Fertilization is more frequent for abundantly flowering plants or annuals, and less frequent for succulents and desert plants.
Also remember that the first feeding after transplanting should take place after 2-3 weeks.

Get the timing right when you apply nutrients. Do not fertilize your plants on hot, sunny days. That way, you can hurt and burn your plant.
It is best to fertilize your plants on cool, cloudy days, in the morning or evening.

Do not fertilize plants on dry ground. Make sure to water your plant at least a few hours beforehand.

After spraying the fertilizer, re-spray the plant with clean water. This should be done after a few hours. This way, you reduce the risk of leaf scorch.

Apply only those elements that your plant needs. Do not substitute one element for another, as you could lead to an excess of one or the other mineral.

Feed only healthy plants. Does not apply to diseases associated with a lack of elements. If you have even a suspicion of disease, fertilizing is forbidden. It is also forbidden to fertilize plants that are sick or have pests.

Never make a mixture at random. Be sure to use a measuring device or you could over-fertilize, resulting in an over-fertilization of one element or another.