If you play carbon-based, you are at a severe disadvantage at the moment. While aquatic can build their special farms anywhere and the other two don't need food at all, carbon-based has to rely on finding arable land tiles in order to get food.
In singleplayer it's not quite that bad though. There is the Galactic Wonder Kimberly's Refuge (the AI seems to not want it so you can always get it), which you should build ASAP on your best food planet. Use adjacency bonuses (from arable/farms, colonial hospitals, cities and colony capitals) to significantly boost Kimberly's food output. Then assign farmer citizens to the planet you built it on. This way you can build enough cities to pop-max at least your homeworld and a few key worlds (i.e. your best planets). There is also a tech that gives +1 food to all your planets.
It has become harder now to keep your people happy (introduction of tax rate in 3.0 and its accompanying morale penalty, introduction of colony limit in Intrigue). I suggest to build morale improvements immediately on your colonies after the initial manufacturing-enhancing buildings, so that you can increase tax rate. At the very beginning, you can set tax rate to 0 to help with morale (if you don't play a Content race), it doesn't give much money early-on anyway. Also, research morale-boosting tech (e.g. "Easy to Please" tech!) and make heavy use of mercs and government ships that boost the morale of the planet they get stationed at. There are also celebrities and leaders.
In the long term, it should be your goal to get both 100% approval and 100% tax rate (or whatever rate you're comfortable with roleplay-wise) on all of your planets.