Ihram means the intention to enter a ritual and it is derived from the word ‘At-Tahreem’ which means entering what is prohibited. Therefore, as you enter the Ihram for Umrah , certain things become prohibited which were permissible before like sexual advances towards your wife, wearing fragrance, shaving the head, cutting hair, game hunting etc.
A person should wash himself thoroughly which includes removing hair from the private parts, trimming moustache or cutting of nails, before assuming the state of Ihram. A complete bath or ghusl should be performed. If you’ve already taken the bath then perform ablutions. Now take off your stitched clothes and change into the two white sheets of the unstitched cloth. Wear one sheet around your waist and drape the other one on your upper body. You can also wear a belt around your waist to fasten the cloth.
Women can wear regular stitched clothes. Ihram for ladies / women pilgrims includes a plain regular dress but most women wear an Abaya with Hijab. A woman cannot wear a veil around her face whilst in Ihram.
Offer 2 raka’t nafl, if it is not makrooh (undesirable) time, with your head covered before declaring the intention for Umrah. It is better to wear Ihram from home or airport and then declare the intention after reaching Rabigh which is a Meeqat for pilgrims who arrive from the UK. However those who are travelling to Madinah first should consider Madinah as their Meeqat. Again, it is better to declare your intention for Umrah after reaching the Meeqat.
Note: It is recommended to consult and seek an opinion from scholars on doubtful Islamic matters.