At a beginner level, my advice is to not rely on one feature alone, but a combination of everything - structure, flight pattern, plumage, habitat etc. If you see a distant bird and can only see structure for example, no problem if you can't distinguish. Wait till you see closer birds where you get all features, then the identification is easier - as you develop, you'll get a feel of the species and slowly you'll get better at distinguishing them at bigger distance or when only a few features are visible. Even then, all of us will sometimes see distant raptors that we don't identify.
If you're looking to distinguish Goshawk from Honey Buzzard specifically, I'd say start with the skill you have ...you are familiar with Common Buzzard, I assume you are familiar with Sparrowhawk. Look through Birdforum and you'll find there are very rarely questions asking for help separating these two ...but there are often threads asking if a bird is a Sparrowhawk or Goshawk, or if a bird is a Common Buzzard or Honey Buzzard. Thus, these are the confusion species - if it +/- looks like a large Sparrowhawk, it is not going to be a Honey Buzzard, but might be a Goshawk. Same with a potential Honey Buzzard. Learn the differences (not only structure, but as much as possible) between these pairs and then start intensively watching Common Buzzards and Sparrowhawks. Eventually something will look a bit different, then concentrate 🙂
If all else fails, take a bus up to Vilnius, I'll give you a weekend training for free 🙂