Bluetack, tape and Velcro can all damage plasterwork and your tenancy agreement may have a clause forbidding their use. This is another thing to ask your landlord, who may agree that if you promise to rectify any damage you cause before moving out. If they say yes, try using ‘damage free hanging strips’, which use a removable adhesive to attach a hook to the wall. Just be sure to check the ‘load’ weight before use.