Always use a Shoe Horn.
A shoe horn prevents you from crushing the stiff heel section of the upper (know as the ‘quarter’ part of the shoe). Additionally, its much easier to put your shoes on with a shoe horn and extends the life of the shoe.
Conditioning your shoes with a product such as the Saphir Renovateur ensures that the leather remains soft and supple, which prevents cracking and helps the shoes mould to your foot. Polishing, apart from its clear aesthetic benefits, helps to seal in the essential oils as well as protecting the leather from dirt, water and other impurities.