Whenever you want to take a screenshot of your render window without positioning a camera first, here’s a simple way of doing it.
Click on the show overlays button in the upper right corner to toggle overlays off.
While in object mode, click on View menu up to the left, then viewport render image.
In order to save image, use the hotkey Shift-S.
Choose a location on your hard drive where you’d like to save your image.
Hit Escape to exit from image view (or choose the 3d-viewport in the upper left corner menu).
When you are done with your screenshot spree, remember to toggle overlays on again…
For more tutorials check out my Youtube channel.