It depends a lot on your country and year. A starting point is something like:

6 motorised infantry battalions (shock if you are investing in SMGs as well as Rifles) - replace with mechanised when available but mechanising supports first seems better value
5 armour battalions (light, medium, close-support, cavalry, heavy, infantry all depends what is available)

Supports

Mechanised HQ (cars until you get that)
Mechanised Logistics (motorised until available)
Armoured combat engineers (motorised until have ARV)
Armoured maintenace (plain until get ARV)
Light AA cars
Armoured engineers (motorised until get ARV)
Either A/C or motorcycle recce

I tend not to include AT (tanks cover piercing), Hospitals (dilutes org too much), Heavy Art/AA (speed reduction)

You need to pay attention to the speed of everything that goes into the division. Generally you want to keep at 9 kph. If you have a lot of slow tanks (e.g. USSR light tanks) you might use semi-motorised infantry and go with 6.5 kph.