After you successfully cannulate the vein, the most important factors determining if it stays in (I.E., doesn't extravasate/infiltrate/dislodge) are the length of the catheter and the distance of the vein from the surface.
Here's the bottom line:
If the vein is <1 cm from the skin, standard IV length will probably be fine
If the vein is > 1 cm from the skin, you need a longer IV catheter.
Check out the video for more specifics!