The default bed temperature for PLA is 60 C, which is generally be sufficient heat for adhesion if the bed is the right distance from the nozzle. However, there are other factors that can contribute to poor adhesion, including the geometry of the print, the presence of supports, the presence of brim, and the cleanliness of the glass. If you're having trouble with adhesion on an ABS print, please check the ABS section of the main Bed Adhesion page for suggestions with this material.
Solid Base, No Supports
The Aria Dragon, created by Loubie and found here on YouMagine, is a fun print that's designed to print without supports. Because all of the overhangs are about 45 degrees, the layers are able to build up and out well enough to print without supports. Something with a steeper angle would require supports in order to print well. The base of the print, even though fairly small, is solid on the first layer, and so it printed well without needing any sort of brim for good adhesion.
Holes in the First Layer
This Earring Holder by ErinMakesStuff on YouMagine (Source File) was printed with the flat side down, so there were no over hangs, and with a very slow bottom layer. If you look closely at each of the holes, you can see where each hole was outlined on the first layer before the rest of the flat surface was filled in. With this sort of print geometry, you need to print the bottom layer very slowly in order to print one of these disconnected little outlines from coming off of the bed. You could also try using a little glue to help adhere it based on the instructions here. Since the bottom of the print was flat, and mostly solid, this piece printed well without a brim.
Large Overhangs, Needing Supports and Brim
Printing mcrockeruvm's Unicorn, found here on Thingiverse required both supports for the legs, and brim to help keep those supports adhered to the bed. Because the unicorn's front legs are complete floating in the air (from the prospective of building the print up from underneath), this print needs to print with supports. You can turn on the support option in Cura's basic tab, and either choose "Everywhere" or "Touching Build Plate." The "Everywhere" option will create supports on any overhang over a certain angle (you can set this angle in the Expert settings), whether that part is over another part of the print, or over the bed. To check out which parts of the print will be getting support after you've turned on your supports in Cura, click the View Mode icon in the upper right hand corner and choose "Layer View." Make sure that at the bottom of the sliding scale for the layers on the right, you have "Multi Layer View" selected rather than "Single Layer."
Touching Buildplate--The "Touching Build Plate" option will only create supports over empty build plate, in this case, just supporting the unicorn's front legs.
Everywhere--If you want the chin and belly of the unicorn supported as well, you'll need to turn on the "Everywhere" option.
When I printed this Unicorn with "Touching Build Plate" supports, the print failed, because the supports had very little surface area and didn't adhere well to the bed, resulting in a bit of a mess about halfway through, and an aborted print.
I sliced the file again in Cura, turning on the "Touching Build Plate Supports, and Brim for Platform Adhesion under the first tab of the Basic settings. The teal color in the layer view represents any supports or platform adhesion layers created by Cura.
The resulting print was considerably better. My unicorn had a little bit of a beard under it's chin, which probably could have used supports, though the belly printed okay. Turning the brim option on anchored the supports well enough for the print to finish. Please note: Cura includes brim on support structures if brim is turned on; some slicers only include brim on the main part of the print, so check your slicer settings before leaving the print alone if you're not sure.
Complicated First Layer with Lots of Disconnected Holes
The butterfly napkin holder I printed, designed by TanyaAkinora and found here on Thingiverse by far has the most complicated geometry of any of the prints on this page. Because of the shape of it, there are a bunch of disconnected pieces on the first layer, which is what makes the adhesion so tricky. I generally recommend 20mm/s as a good rate for the bottom layer of prints. However, with that print, I slowed it down to 5mm/s for the bottom layer to make sure that the filament had plenty of time to cool and would remain stuck. I might have been able to speed it up to 10 or 20mm/s for the bottom layer if I'd had used glue. The 2 butterflies seen here, and the bottom piece all printed flat on the print bed and were assembled afterwards. No brim or supports were needed, but slowing down the first layer was crucial to getting this print to come out right.