This largely depends on the application and final effect wanted, but an easy way is double sided sticky tape.

It is also possible to temporarily fix our standard product using LEE Gel Fixing Spray, available direct from LEE Direct. 

It is difficult to recommend a glue. We have tried many and have not found one we could recommend. Many glues solvents that can attack the coating on Lighting Filters. This damages them.  

If you need to try a glue we would suggest you try a water based one.  It does depend on how permanent you want the join to be. Please try a small area first.  Please also follow the glue manufacturer's instructions.