There is no one simple answer and no universally correct answers to this question. You need to understand all the settings on your camera and you need to understand the relationships between Aperture and shutter speed which allow correct exposure. I would strongly recommend you read some good books on basic photographic technique rather than taking a straw poll of opinions.
This said here are a few basics that I use :
I shoot in shutter priority mode and generally set a speed of 1/500 or faster for jet aircraft. However this is with the proviso that I can still get an aperture no wider than f7.1. If I am having to go wider than f7.1 I will drop a shutter speed.
For prop aircraft I shoot at between 1/200 and 1/320 to ensure prop blur.
If you are shooting in Aperture priority you should normally aim for an aperture of around f8 to f11 as this usually gives the best performance from the lens. I would strongly recommend against shooting at the widest aperture (lowest f number) on the lens as this is likely to increase distortion and give poor depth of field.
In simple terms aperture affects depth of field and the bigger the f number the greater the depth of field but as I say optimum lens performance is usually around f8.
Shutter speed affects camera shake and the ability to freeze motion. For hand holding the rule of thumb is to set a shutter speed greater than the focal length of the lens in use to avoid camera shake. Thus for a 100 mm lens you want a shutter speed of 1/125 or greater and for a 300mm lens you want 1/320 or greater.
The above are just rough guides. All situations are different so like I said at the start read some books to get an understanding of the basic principles. Make sure you fully understand all the controls and settings on your camera then go take some pictures. Look at the results and try to analyze and learn from your mistakes. All this will take time - there are no instant answers.
One final thing - above all else - have fun and enjoy yourself !
One thorn of experience is worth a whole wilderness of warning.