Check the seasons. This can be done with computer modelling and space scanning. You want a place that has warm summers, cool winters, minimal rain, and few storms. If a place is filled with storms, is too hot, is too cold, or is constantly raining colonization will be harder. This can be done with a few satellites.
Check if there are any civilizations or local competition. You can stick a few spy satellites in space and map out the planet in depth.
Check the atmospheric composition. You want to know more than the oxygen level. You want to know anything else useful.
Check the local star, local asteroids and everything nearby. You don't want to land and then have a large solar flare wipe you out, or have an asteroid hit your planet.
Next, you can land a bunch of drones in places, with curiosity style bodies.
Check the tectonics. You want to put probes in a bunch of places and check for earthquakes or disturbances. This will allow you to map out what is going on under the surface. You don't want to stick a colony down and have a volcano erupt or a massive earthquake wreck you.
Check if local organisms are edible. You'll want to send a probe down to kill a few insects or small animals and plants (or the local versions) and test if they have the right chirality, anything especially toxic.
Check if the land is able to grow earth crops. This will involve a variety of chemical tests which your probe can probably do.
Check if there are any obvious useful minerals around to build a colony from. This will involve scanning with a bunch of tools.
Check for any trees or similar things that can be used as building materials.
After this, you'll have a bunch of likely candidates for where a colony would be best. If you don't and it's a horrible planet, you might decide to not colonize it.
After this, you pick the best candidates and send a bunch of UAVs.
Unmanned aerial vehicles. These would have solar charging, and could fly around the area and scan for any local organisms, mineral deposits, signs of life, or other useful or bad things.
With the area mapped out, you can send a small human scouting force.
This will be a few humans who have a deep knowledge of biology and chemistry. They can map out any hostile insect swarms, large dangerous predators, hostile micro-organisms, and likewise any useful organisms, local compounds, local minerals. They can do more in depth scientific setting and set up any infrastructure needed for a full colony. Any dangers the previous layers didn't reveal will hopefully be exposed now.
They can also set up camera networks around the area. If there's any hidden predators or intelligent life nearby, then they may well be spotted on the cameras when they don't think they're being watched.
Or they might be killed, but that's why you send a small force first.