Not a resident, but I have spent some time up there.
Glasgow - Eastern end of Sauchiehall Street, Buchanan Street area good for shopping. Merchant Quarter or West End good for pubs and restaurants. Kelvingrove Park has art gallery/museum and close to University buildings. Necropolis is interesting to those with a gothic bent!
Edinburgh - Old Town, Castle, Princes Street, Arthur’s Seat, Calton Hill, Holyrood. Leith area good for pubs and restaurants.
Highlands - big area, will need independent transport to get around, but some trains out to Fort William at the top of Glen Coe and “close” to Ben Nevis.
Comfy waterproof walking shoes for cities, stout ones for the Highlands. Light waterproofs and layers for warmth recommended. Weather is warmer and wetter in the west and windier and chillier in the east as you might expect.
A Lonely Planet guide or similar recommended so they can choose things that interest them.
In terms of safety, dark streets late at night best tackled in a crowd. Don’t go mountain climbing in T-shirt and trainers. If out in the countryside or hills, ensure someone knows where they are going and when they plan to return. Basic common sense really.
A Real Expert will be along shortly, but hope this helps in the meantime.