which levels are you specifically referring to? I have not played through the entire game yet, but I have found getting gold to be fairly easy.
The levels that require certain objectives to pass I have found it is best just to focus on them and not worry about picking up corn as the gold should come naturally. For the ones that dont have set objectives and only a certain amount of corn, focus more on the corn. Try to pick up the negative boosts which increase your multiplier. Though going fast with your chicken earns you a x2 multiplier, I find it best just to go quite slow to avoid dying. Remember the new patch adds +10% to your score at the end for each life you have left. This is key to success and making this game easy. Try not to die. Get power ups if you can to increase you multiplier, and focus on the objective if there is one.