I thought I might supplement Phoenix's guide with a couple of extra tips.
How often do you have to log on?- Once every 3 days, but also on the last day of Autumn.
It's worth knowing when the game 'refreshes' - that is, when daily challenges activate/disappear and when the season changes. In the UK it happens at 14:30. Work out when it happens in your region by looking at an upcoming daily challenge and seeing how long it is til it activates.
Daily challenges are active for 3 days. This means that a challenge that activates at 14:30 on Thursday won't expire until 14:29 on Sunday. To give an example of how you can stretch this out and get every daily challenge done without playing daily, you could play the game on a Sunday morning and net the daily challenges for Thursday, Friday and Saturday in one sitting. Hang around for the refresh at 14:30 and complete Sunday's challenge. Finally, come back Thursday morning to finish off Monday, Tuesday and Wednesday's challenges.
The times will change depending on your region but as you can see, you technically only need to log in twice/3 times a week. You don't need to stick to this routine either, but just make sure you bear these times in mind and just make sure you log in at least every 3 days.
Important! You must log in before the new Summer season activates and complete the Autumn daily challenges. Because of the 3 day cycle, it is technically possible to finish Autumn's daily challenges 2 days into Summer, but the achievement will be void.
Playground Games - do I have to? - Yes, but it can be surprisingly painless.
This is down to luck, but you can use good judgement to ensure you waste the least amount of time.
People on losings sides quit. The smaller a team gets, the more difficult it is to win, the more people quit. In my experience most of these games end because an entire team disconnected, which spells an automatic win for the remaining team.
So what can you do? If you find yourself unlucky enough to be on a losing team, don't fight it. Just quit and search again. Soon enough you'll find yourself on a winning team.
Not much to add here, except: This is a team game! Race cleanly with your teammates! If you and two other teammates are in 1st, 2nd and 3rd, it doesn't make a difference who comes where. So don't jostle for position and risk messing it up for all of you. And if you find some idiot on your team who is ramming and going for glory, give them a wide berth and let them pass.
As for your opponents, they're all AI, so race them as dirty as you like.