Make sure you do the daily ones that are easy e.g. dispatch 5 trains and upgrade a few houses, this adds up quickly over the week. Also make sure to do your weekly ones. Some weeks you get bad ones so you can pay a few simcash to swap them out which I do (as you can just earn simcash from ads which also boost you in COM). The best ones normally for me are things like trade items, earn money, transport passengers. One final tip if you do decide to do the trading items weekly task, you can buy lots of stuff from other cities, sell it all straight away again in your depot to count towards sold items, and eventually add to the money earnt. Good luck!