1. for buildings,put 1 layer of cobblestone for the base of a wall and put oak planks on top of that, use Oak Stairs for roof.
s. A 5 to 8 high cobblestone wall around the outside of the town.
3. little outlying farms outside of wall with small huts made from oak planks
4. Make streets from gravel 2 wide with a 5 wide for 'main' street
5. Put a tower in the middle of the town (6x6 base, 16 high and make the floor on top stick out 2 blocks from the wall)
6. Put a barracks near the tower. Build it so you can put about 10 or 12 beds per level (make it 2 stories)
7. Make a gate from 2 iron doors. You can come up with you own little opening device (without making it too easy for enemies to open doors)
And see if you can't spawn some NPC villagers inside the town. It'd make it realistic.
Past the basics, make it interesting with your own ideas. Put signs on the buildings, make each one a specific building (blacksmith, market etc.) and put other buildings with beds in them for houses. This give you a good start?
Military riverside village. Short wooden structures with cobblestone foundations. Wooden walls surround the city with 4 gaps, 2 for the river and 2 gates for the road passing through; a trio of watch towers guard the perimeter. Buildings of note are the watermill, soldiers barracks, stable, trading post and black smith.
Mining post in the snowy mountains. Wooden shacks with supports to keep them flat on the uneven ground. The post has no boarders except for where the torch-lampposts stop; a single tower stands tall in the center of the town (used as both a watch and clock tower). The only buildings to note are the miners huts, trading post/smith, and a mine entrance.