Bacteria and viruses are microscopic, so cannot be seen with the naked eye.
If possible, it is best to inject in a private space by yourself to reduce the risk of blood contamination. You should choose a hard surface (bench or table) that is free of clutter and can easily be wiped down. You can use soapy water or alcohol swabs to wipe it down.
If you are unable to inject in a private space (for example you need to inject at the gym), you have to be even more blood aware. Do not inject other people or have them inject you and do not share any equipment. Make sure you carefully wipe down all surfaces before and after injecting.
Make sure you wash your hands thoroughly with soap and water for at least 20 seconds before setting up.
If you can, wash the injection site on your body with soap and water as well. This is better than using an alcohol swab, though you should use a swab if you cannot wash the site immediately before injecting it. Use one swab in one direction only so you are not wiping dirt or bacteria around and allow it to dry before injecting.
You will need a sharps disposal container on hand to dispose of all equipment before you start injecting.