If you are new to macro photography and having a hard time deciding which f/stop to use when shooting a subject, just shoot a wide range from the smallest f/stop number to the highest f/stop number, and than decide what worked out the best when you get home. The smallest numbers will give you the least amount in focus and the highest number will give you the most in focus.
Here is the first shot using the smallest f/stop with my Tamron 90 at f/2.8.
Next I used f/8. Adds a little more in focus.
Next I used f/11. Adds a little more in focus.
Next I used f/22. Adds a little more in focus.
Next I used f/32, for the most depth of field and the most in focus.
You can decide what you like best as far as how much of the subject is in focus when you get home and on the computer. Pixels are free to shoot, so why limit yourself to one f/stop, when you can give yourself more options if you’re not sure which f/stop is the best choice for the look you are after.