Keep doors closed and make sure draughts are reduced as much as possible.
If you have any windows/outside doors that don't seal properly around the outside you should get that fixed as it's the easiest place to leak warm air out/cold air in.
If you own the house or can convince the landlord a longer term solution is to improve the insulation in the walls. Similarly avoid rooms with large windows because they leak a lot of heat.
If you have blinds/curtains in front of the window keep them closed and that will trap some cold air behind them from the rest of the warm room.
When you move try to avoid detached houses as it's much harder keeping a house with more outside walls warmer. An apartment sandwiched on all possible sides is ideal.
Basically, heat up a bunch of air and don't let it go.