I think you could resize the just a little bigger.
Think of you camera and 300 lens like a shotgun as it will only shoot out to 50 yds with any clarity for a decent crop.
You can try the Sports mode if the subject is moving or the Landscape mode first.
I prefer to set up the cameras menu first to the finest setting JPEG set up some contrast, little color saturation and some sharpness, leave the ISO to auto and set the focus to Spot and the metering to Spot also. ( for more advance shooters They can use the bracket feature where it shoots 3 pics at once at different EV and you can pick the best pic)
Lighting is the best way to get a good pic with most lens. Make sure the subject is not in the shadows and with the sun lighting the subject (preffered at your back or a quartering shot).
I like to shoot at either Program or Aperture Priority mode once you have your menu settings set up.
Program mode is a deluxe point and shoot with favorable results as the camera will compensate for shutter speed and ISO<EV and Fstop settings..I like the Aperture priority mode along withe preset menu settings and can set the aperture opening Fstop usually around F8 on most 300mm lens with the IS turned on.
Once you get more experience and can afford more memory and a good RAW editor some guys shoot in RAW format or RAW and Jpeg format and actually develope the picture with software to their liking and perhaps come out with a better pic as it is not compressed.
Advanced shooters use a circular polarizer on some water shots but you would lose one F stop and make adjustments.
You know you have a keeper lens when you can shoot it in diferent zoom ranges and the pics come out sharp with good colors and Bokeh with the menu setting and do not have to go thru the photo editor also if the pic comes out favarible even at 100% crop
Some shots with the 70-300mm:
some close shots with good lighting
last two shots are at 60 yds and 120 yds with a little cropping