Singular and Plural
This goes for table names, and also for the names of join tables. If you call your tables "user" and "group" then you probably want your linking tables to be "user_group". If you go for plurals (my personal favourite) then be consistent over whether the linking tables are called "user_groups" or "users_groups".
I've seen two main variations on the column names for primary keys, one is to call them all simply "id", and the other is to name them after their table name such as "user_id" or "group_id". It doesn't really matter but my recommendation is for the latter - that way, the user_id column in any other table clearly joins on to the user_id column in the users table, making it easy to read and understand.
Case and Capitalisation
Due to my EXtreme DOuble CApitalitis, I prefer everything to be lower case, but the key is consistency, so that it is easy for developers to get used to the patterns in the database setup and to develop against your schema without having to refer back to it all the time.
Consistency is Key
In general, I like database schemas which are predictable and well-laid-out. Although I have my own preferred conventions, I don't mind what is used so long as it is predominantly in step with itself - this makes my life as a developer so much easier! What's your top tip for sane database naming conventions? Leave a comment and let me know!