Advance the catheter into the place where you visualized or palpated the vein. Once you receive blood back into the hub of the catheter, slowly feed the catheter off the stylet and into the vein.
If you hit resistance, pull the catheter out of the vein and back onto the stylet. Ensure that blood is still backing up into the hub of the catheter. If it is, gently advance the catheter and stylet a little more into the vein and try again to feed the catheter into the vein.
If no blood is backing up into the hub, pull the catheter and stylet out until you see blood flow into the hub. Attempt to feed the catheter off the stylet again.