Can anyone give me some advice

Some tipps:

• higher ISO means more noise, for Adobe stock you absolutly need to keep the noise low.
• low aperture means low DOF. For some subjects, like the bee, it may be needed to get the whole subject in focus.
• ISO, aperture and exposure time go together. You should know, when the noise starts coming. You should know the focussing depth for a certain lens and aperture. And you should know at which exposure speed you still can make good handheld photos. And you should train to shoot with manual settings. It's not that difficult. Setting the aperture and the speed manually will beat the automatic settings.
• To check exposure, check the histogram. The histogram needs to touch each border, without having clipping. (The dark side is to the left, the light side to the right). 
• You can use a high(er) ISO at a familly gathering, but avoid it when you shoot for stock. If you have a high ISO, you will need a good noise reduction algorithm.
• Changing the lenses are critical operations. Don't do it in dusty environments. I once changed my lenses in a workshop. In addition to having dust, the dust was also contaminated with oil. It ruined the sensor. Since then, I change the lenses only when needed (I use mostly prime lenses, no zooms!), and I am careful to do it in a protected environment and as fast as possible, holding the camera down. 
• To check the dust pattern, take a long exposure picture of a white or light background with the focus completly off. You will get a white image with the dust stains. 

You need to shoot raw and you need to edit all your pictures on the computer. For that, you will ned a special program, like Lightroom (Classic), Adobe Camera Raw (comes with Photoshop and Photoshop Elements), or similar. Canon comes with DPP, which is OK, but as soon as you have access to a third party program, you probably won't use it anymore.