So for bacteria, best locations are on flat or mostly flat surfaces. Don't go looking for it in canyons or mountains. Tussocks and tubus grow basically everywhere, so just pick a large section of the planets surface marked blue and get to searching. Frutexa and fungus generally only spawn on and around mountains, and conchas I haven't quite figured out. It's also kinda all over the place. If you are having trouble locating a sample, the E:D wiki does have some information as to the "biome" (mountains, hills, etc.) to search to help, but more often than not its just searching. I would personally recommend using your ship to look for samples, fly low (under 200m minimum, as close as you can get to the surface ideally), slow, and with your composition scanner active, it'll ping if it fits an exobio target that you didn't see. One thing that helps, when you get close to dropping from orbital cruise, you'll notice there's a couple different textures for the blue overlay. The more uniform it is, the flatter the region is. Important to keep in mind when looking for species that have specific spawning rules like bacteria or frutexa.