Minecraft wiki entry for Creating_a_village, associated text: You can recreate natural village buildings as much as possible, but for example, building another temple does not create more clerics; for that you need to add more brewing stands, that being a cleric's job site block. More villagers simply means the babies produced have an equal chance of getting any of the occupations that depend on the job site blocks in the village.
You may be interested in building a villager farm; they produce villagers in extremely high densities, making it worthwhile to enclose the entire villager farm to keep out hostile mobs and make it easier to light up and navigate.
Villagers tend to be careless. They can fall off from high places, take damage on cacti or even swim in lava pools. Restrict them from such areas as much as possible by placing fences or any other kind of barricade (other than cacti, fire, or lava).
You can add fountains, trees, parks, and the like to beautify the village.
When night falls, villagers fail to scatter around so that they all go into a different house. Villagers seek unclaimed beds, which means if a villager cannot find any unclaimed beds, most of them would probably fail to get into the safety of their houses. To prevent this, one can make a big house with more than one bed. However, another way of protecting them is to simply sleep before hostile mobs spawn.
Create lamp posts. This reduces the number of mobs that spawn. A plains village lamp post is usually 2 fences and a block of stripped oak wood on top, with torches on the sides of the wood. Another design could consist of (savanna village design) acacia fences and torch on top of it, (desert village design) terracotta on top of 2 cut sandstone with a torch on top of terracotta, (taiga and snowy taiga design) cobblestone wall with a torch on it, (snowy tundra design) 3 block height of spruce fence with 1 to 4 lantern attached to the bottom of sided fence (or if you are lazy, just place a torch every 10 blocks). Once you've gotten pumpkins (the Wandering Trader can help), jack-o-lanterns become an option.