It is a tough question as there are many roads to success in this industry and all of them have traps and road blocks along the way.
I would encourage someone to AVOID any site that forces you to view someone else's ad in exchange for sharing their own ad ONLY UNTIL they have a clear business plan and strategy in place. Hopefully this would allow them to skip the rabbit hole of program hopping or shiny object syndrome and give them enough time to research (via blogs, forums etc where it may be 'easier' to avoid being sucked in to the hype of ads you will find there).
Once there is a strategy and plan in place, which can always (and should in fact) evolve over time that is the point that exposure to the endless "opportunities" will be easier for someone new to the industry to navigate. They will have more focus and be more invested in their own plan and strategy and therefore only join programs or opportunities that are of actual use (yes, ad exchange platforms are fine at this point) or supplement and support their own business plan and strategy.
Additionally I would recommend they find a mentor who is genuine in mentoring (as opposed to sponsoring) the new comer.
I realise these thoughts may be contrary to what many here would like to see and I do see a place for ad exchange platforms, just not as the starting point.