Describe the problem before adding anything
A compost bin that looks inactive may be too wet, too dry, poorly mixed or simply working slowly. In a UK or Irish garden, inspect material below the surface and note what has recently been added. Rain on the lid does not tell you the condition inside.
Keep a mixture you can manage
Avoid adding only one large, compacted type of material repeatedly. Keep suitable dry, structured material available to combine with wetter additions. Check local composting guidance for accepted inputs and keep unsuitable waste out. Cut or break bulky garden material where it is practical and safe.
Make one adjustment and observe
Improve the mixture or moisture according to the problem rather than adding several supposed activators. Keep the bin accessible for routine maintenance. A manageable amount of material with a repeatable process is more useful than a large neglected heap.
Allow for the conditions
Decomposition does not follow a fixed household timetable. Note changes in texture, smell and the recognisability of ingredients. Use mature material appropriately and seek advice if contamination is suspected. Keep a separate disposal route for items that should not enter the home compost system.