I combined some great recommendations I found, enjoy :)
What You'll Need:
* An open glass container (tall, small, or even mason jars)
* Twigs, driftwood, seashells, small rocks, sea glass, and memorabilia
* Smooth stones
* Air plants (ephiphytes tolerate infrequent watering and indoor lighting, you can also use: tillandsias, dischidia, hatiora, and other succulents)
* Store bought sand from a craft store (can't use actual beach sand sorry!)
* Rainwater or filtered water (avoid tapwater it has salt minerals in it)
* Charcoal or premium activated carbon pieces if desired to keep mildew away
Step 1: Places stones and sea glass on the bottom of the container
Step 2: Spread about 1-2'' of sand on top of the stones and form a mound in the center.
Step 3: Insert plants (succulents or cacti) halfway into the sand in the center of the container.
Step 4: Soak seashells, driftwood, etc in water for a few minutes to remove any salty residue (bad for the plants)
Step 5: Insert the seashells, driftwood, small rocks, etc around the terrarium
Step 6: Water just once a week!
Here are some decorating ideas for your beachy terrarium. Remember, an open container terrarium has a totally different care level than a closed terrarium due to the build-up of moisture instead of the sand and stone based mixture in these terrariums that have an opening for the water drops to escape out of.
Enjoy making yours!