All condoms should carry an expiry date on the box and on the wrapper that contains the condom itself. You should always check this, as expired condoms may not work effectively. Always use known brands that carry a CE mark and British Kitemark. You should always make sure you are wearing the right size. The standard size should fit nearly all men, but small and large condoms are available.
Use a fresh condom every time you have sex and make sure it is put on before any sexual contact. Roll the condom onto the erect penis and keep it on until ejaculation. If having vaginal sex, you should withdraw before the penis goes soft or the condom could slip off. Do not use petroleum or oil-based lubricants such as vaseline or baby oil, as these can damage condoms. Safer water-based lubricant is available from all chemists.