The jubilee clips on the coolant hoses are often known to be on the lose side, make sure they are all pinched up. Failing that it's just a case of checking everything such as the cap on the radiator, around the water pump gasket area, the hoses for splits etc. The chances are that once it's up to temperature and pressurized you should be able to be spot a leak fairly easily, it's more difficult if it's weeping because it can evaporate quickly on a hot engine.