The contract should contain the following:
the sale price
the property boundaries
which fixtures and fittings (like carpets and kitchen units) are included
any legal restrictions or rights, like public footpaths or rules about using the property
any planning restrictions
services to the property, like drainage and gas
when the sale will complete
You want to check all these, the important ones are:
Property Boundary - You want to check the drawing matches the existing fencing, building curtilage as you don't want to end up with a neighbour making a boundary dispute down the line.
Fixtures & Fittings - Should have been discussed at offer stage already but ensure it matches any agreement made. It may sound simple but if it's not specifically mentioned in the contract the seller can take it with them and it's a pain to have to get new carpeting/light fixtures/any white goods if you haven't specifically allowed for them.
Legal restrictions - Fairly obvious, make sure there aren't any utility wayleaves etc (things like water mains etc running through the property boundary) as these would restrict any future development/extensions etc. You'd also have to make reasonable access available to the owner of the utility if there is a wayleave. Some areas also have restrictions on smoke (no open fires/chimneys etc), what you can/can't install on the building (could include items like satellite dishes etc).
Planning restrictions - Similar to above, your solicitor should make you aware of any planning restrictions on the property.
Services - As above, just check it matches what you are expecting. If it's urban there should already be existing electrical, mains water and mains drainage along wiht telecoms and mains gas. If it's rural, electric is a given but you may not have a mains water supply (could be borehole etc), may not have mains drainage (could be a septic tank) and gas may be bottled supply rather than mains. All of these have different costs to mains supply and also normally require annual maintenance and associated fees.
Completion Date - Pay attention to this one!! Make sure it matches when you expect.
As a general rule, your solicitor should already have reviewed the draft contract and should make you aware of anything of significance but ask for a quick rundown of the above items.