After many unsuccessful attempts at collecting Cleome seeds I discovered a little trick. I'd go out and pull what to me looked like a ripe seed pod only to discover that the seeds were still white inside. What I found was that if you take a seed pod in your thumb and forefinger and gently squeeze if the pod is ripe it will start to split. If you apply pressure and it doesn't split in your fingers the pod should be left and checked later.
While looking for places to dry seeds I had collected I ran out of paper plates and used an envelope from some junk mail I had received. The envelopes worked great because I could set many of them in one spot side by side and because they are made of paper they absorb the excess moisture on your seeds or seed pods. When the seeds are dried you can take the paper envelopes and compost them.