Basically, the wider the appature, the less is in focus (depth of field).
I tend to use either TV or AV mode the most. If you want to control the depth of field select AV mode and then if you want more in focus, choose a nice small apature, while watching the length of your exposure. If you have an Image stableized lens then you can usually go down to about 1/10 second exposure if you have steady hand. Slower if you have a mono or tripod.
Increasing the ISO setting can let you choose a smaller appature also.