These two are more difficult than most people admit to, steer clear of size and the supposed upright stance of the Mistle that can be very confusing.
You picture in my opinion is Song, but pictures can lie, here goes, white under throat, white eye ring, pale brown back, small under carriage spots arranged in streaks not random as in the Mistle.
If your bird flew the under wing should have been creamy, to me the white throat is the obvious sign.
It's just practice and being happy to make mistakes.
I agree Song Thrush and if reasonable views I found the distinctive creamy edges (middle coverts I think) on the species another way to help ID.
Hope you did not mind but I took your image and added ta box to help show the markings.
It's a period of time that is probably one of the more special times as you start learning about the ID of certain species that only comes as a newer person to birding so enjoy it as Greengrass says....although knowing what you are looking at intensifies that feeling.
