To piggyback on the first tip: when you finish The Brrrgh, you're in a good position to train your gags as you'll have all the tracks (except the one that you didn't pick); It is worth training your gags a little before starting the Donald's Dreamland tasks as many DDL tasks are centered around Cashbot HQ which is tricky if you have weak gags, especially when it comes to finding groups for the mint and CFO.

When you're training a new gag track then the best thing to do is to go to a district with an invasion (These can be found using the ToonHQ invasion tracker) and then go to Welcome Valley, this will take you back to Toontown Central where the cogs are level 1-3 but you will still get double experience. Once you've got the gag up to level 3, look for 4-5 story buildings in districts with low level cog invasions and use that gag throughout the building, repeat the process and you'll max it in no time.