For doors with handles that open outwards, tie one end of a cable lock around the
door handle. Tie the other end to a structural support (eg a pillar) or other fixed
point. If no structural supports are available, use a piece of furniture or a large
block of wood that is bigger than the door frame.
For double doors, shove a broom between the handles! Even better, use a metal bar.
Alternatively, tie the handles together. Make it tight – there’s no point if the door
can be opened wide enough to cut the rope
For doors with bars (eg fire doors), you can stick a chair between the bars, or tie a cable around
the bars as above - so long as there is space between the bars (image source – Occupation:
a Do it Yourself Guide)
When doors with bars have no space for a cable, secure a G-clamp to the bar. Loop a cable lock (or rope, or cable tie) through the space created by the clamp. Note that some fire doors can’t be opened from outside anyway, and won’t need barricading at all. (image source – Occupation: a Do it Yourself Guide)
Sliding doors can be blocked from sliding open easily, using a block of wood that’s the right size. Many sliding doors can still be pushed open with force, so think about using other types of barricade too.
Attach bolts to a door so you can get out if needed.
Hinges are strong, so good for quickly securing a door to the frame.
Change the door! If it is too hard to secure a door that opens outwards, just remove and reverse the hinges.
Though it takes time, installing a bar across a door adds a lot of strength AND can be removed easily when leaving.
If nothing else works… Build a giant wall of tat. The combined weight stops the door from opening inwards, and if it’s opened outwards things will fall on whoever is opening it. Keep materials on hand to pile on to doors which bailiffs are trying to open.