A further aspect that distinguishes top players from beginners:
A beginner looks at his destination cards, looks at the shortest connection, plans the route and then collects the colors needed for this path (often drawing from the open pile to get the correct colors).
A master rather collects 30 random color cards (from face down deck to improve chance for locos) and only when they know which colors they have available (and which routes are blocked by then) they decide their route. If you have 45 trains to place you can do huge detours - you do not have to connect you cities efficiently.
The planning phase begins *after* you have 30-45 color cards collected!