Purchase condoms that are appropriate size wise and fit well. Ill fitting condoms will decrease sensation. Dont try to impress a broad w/ magnum condom boxes if you cant pull it off.
Engage in foreplay. Extend that if needed.
Lube.
Frame of mind. A majority of erectile dysfunction cases are caused by mental blocks or complications. Its important to be in a positive, happy, and confident space, mentally.
Physically, erections are the result of blood flow. Being in good health matters. Exercise and eat better.