You may cringe, but look at veins on folks in the elevator, in the grocery line, at a football game. Feel your own for that familiar bounce. Think about which way they twist and turn. Take your index finger and obstruct the flow slightly and then feel the difference.
Ok then go with someone who is good at it. Ask to watch quietly.
Then ask that they go with you and watch quietly. Have your equipment, needle, tape, flush, cap etc. Look at the vein and remember how yours felt. See if theirs feel like that. That bouncy, soft rubbery feel. Put on the tourniquet if it is a younger person. Only tie it tight enough to stop venous blood. If you have tostretch it so much it turns into a rubber rope it's too tight.
If it's an oldie you may not need the tourniquet, obstructing with a finger may be sufficient.
Now in your dominant hand look at the length of the jelco/angiocath etc. Imagine how it will feel next to the vein. Then on a less than 45 deg angle touch the tip and commit to the stick. If it's a good stick you will get a visual confirmation.
Follow whatever directions the mfg. says. Never withdraw and restick. Use a new cath each time, and never pull the sharp out and resheath it, you might cut the cath.
SO, research, feel, look, get advice, try, get feedback and you will soon become the one others ask for help with IVs.