When lighting up steps, you need to position the up-light so that it will light the bottom step and "stretch" the light beam up towards the top of the steps. This will need some experimentation before final installation.
The best ground burial low voltage cable to use is a round, double-insulated rubber type with a tough outer sheath impervious to moisture and salts in the soil. The round shape seals well through cable glands or membranes into junction boxes to avoid moisture getting in.
The cable is usually run under ground but can also be laid under bark or gravel. Your electrician will be able to advice you on the safest way to lay garden lighting cable.
Special care should be taken when laying cable for garden lighting to illuminate a slope or terracing, avoiding trip hazards.
Always plan to lay the cables for your garden lights whilst the landscape work is in progress especially if the cables are being laid below the surface.
Otherwise you will find yourself taking up slabs or even footings.
Protective conduit should be used where cable might be vulnerable, for example where it crosses under a grass path where lawn edging during maintenance might damage the cable.
And finally, be considerate to neighbours who will almost certainly not want their garden illuminated by your garden lights.