Not specifically this DW game, but the next one I run, I want to incorporate the skills system from TRoS.
The way it worked was for characters to pick a profession, which gave them a few known skills and left others unknown. To use them, you rolled a number of d10 equal to the related stat(Half stat in DW?) to get equal to or over the skill rating. IE: You have lockpick 7(novice) and a Reflex of 16. You roll 8 or REF/2 D10 and try to get 7 or more. Each additional success made it better, faster, etc. You then make a mark next to the skill if you succeeded. After five marks, you could make a Wits check (Related stat in DW) to improve. As I recall, the number was 15-next skill level. If you rolled 0 or 10 on the D10, you rolled again and added it. So to continue the example above, you just made your fifth successful check and can try to improve the skill and lower future DCs by 1. So for the check, the player rolls 8D10 and needs to beat 15-6 for 9. Next time, the player will need 15-5 for 10, 15-4 for 11 and so on. It becomes increasingly more difficult to reach lower/better skill levels but the rewards are worth it.
To show an change in difficulty during a skill check, the DM will remove d10 from a players pool.