Choose the clip from the work, not from fashion
Every clip is a bargain between sweat and warmth. A horse in winter work grows a coat that keeps him warm standing in a field and makes him overheat trotting up slopes, so you remove hair exactly where his workload makes him sweat, and keep it everywhere he needs protection. A horse hacking gently a few times a week and living out needs only a bib clip, which takes the hair from the throat, chest and underside of the neck where sweat gathers first. Steady regular work suits a trace or chaser clip, which follows the lines sweat takes along the neck and belly. A horse in hard work, hunting or competing, earns a blanket or hunter clip, leaving a protective layer over the back and loins or just a saddle-shaped patch, with the legs left hairy in almost every style for warmth and protection against mud and knocks.
Prepare the horse and the clippers
Clip a clean horse or clip twice as slowly: dirt and grease blunt blades and drag through the coat, so a bath or a very thorough groom the day before pays for itself. The coat must be completely dry. Oil the blades before you start and every few minutes as you work, keep a spare set or a plan for sharpening if you are doing a full clip, and have a rug, a helper and a settled horse all arranged before the clippers switch on. Introduce the noise and vibration against his shoulder first if he is young or new to clipping, and let him learn it is boring before you ask him to stand for an hour of it. Work in daylight or strong stable light; clip lines you cannot see are lines you cannot keep level.
Technique: long strokes against the hair
Stretch the skin taut with your free hand and run the clippers flat against the lie of the coat, in long, even strokes, so the blades cut at a constant height instead of digging and leaving tramlines. Feel the blade temperature against your own wrist every few minutes: hot blades burn skin and sour a horse on clipping for years, so stop, brush the hair out of the blades, oil them and let them cool. Around the elbows, stifle and face, slow right down, pull the skin smooth and take small amounts at a time; these are the places nicks happen. If he needs the head done, many owners leave a half-head, clipping the cheekpieces' line and leaving the face, which most horses accept far better. Build in breaks on a long clip, for his patience and your back alike.
Rug for the horse you have just created
The horse you unclip is thermally a different animal from the one you started with, and his rugging must change the same day. A bib-clipped horse living out may need nothing heavier than before, since most of his insulation remains; a blanket or hunter clip on a horse who keeps working and standing in a stable needs rugs matched to the weather and his condition, checked morning and night rather than set by the calendar. Watch him for the first days after clipping: many horses are noticeably fresher and sharper once the coat comes off, which is information for your schooling plans, not misbehaviour to punish.
Timing and tidying up
Most owners clip when the winter coat is fully through and the horse starts coming back from ordinary work sweaty and slow to dry, then re-clip as regrowth blurs the lines through the season, with the last clip late enough to leave his summer coat undisturbed. Brush or vacuum the clipped hair off his skin afterwards, because loose hair under rugs itches, and check the clipped area over the next day or two for any nick or clipper rash that needs watching. Noting the clip date, the style taken and the rug changes in his KinsLe Care Teams plan means anyone bringing him in or turning him out works from the new arrangement immediately, not from last month's habits.