Each challenge has it's own set of Bronze, Silver and Gold standards. Usually this means to complete the entire match without losing. While some of this is left up to chance, using an anagram solver to match up the highest possible word score will deffinitely help.
Trailblazing - Complete the entire map in one turn. Make a route that leaves open the possibility to back track. Take opportunities to capture prisoners where possible and always use an extra on each turn.
Fightback - I found this to be identical to Trailblazing and the goal of capturing the entire map in one turn. Same goes here to route a path that leaves open the possibility to back track. Take opportunities to capture prisioners where possible and always use an extra on each turn. Tip for the 3rd Challenge, go right instead of left. If you can't win 5v7 you wouldn't be able to finish it going left to start. Save yourself the time of retrying.
Colossal Conflict - Every match up must be 8v8. While the first 2 may not solve the anagram, there is always the possibility. Win each matchup by either solving the anagram or outscoring your opponent.
Prisoner Capture - As the title explains, simply match yourself up against a larger opponent and take the maximum number of prisioners. Very challenging, but go about it the same as other challenges and map out a path to make the most of the map. Do NOT use extras, as the Gold requirements are the maxiumum possible on the map. The challenge is skewed in your favor as the AI will not choose the highest possible word, but don't be fooled they will play high value tiles.
1. Procure Prisioners
2. Captive Audience! - Take the right path first.
3. Convict Capture! - Take the Left path first. A bit of luck and possibly a tie or two. The actual maximum is actually 16. Feel free to use an extra at the end.