Designing a database properly can take some time but it's really not too difficult and will save you time in the long run. This is what I do for a living.
The best way to start is by doing a brainstorm. Let's say I want to design a relational database for a video store. First thing to do is to think of ways to describe a video store and how it operates using nouns and then list them. For example:
the list can go on. Once you have thought of everything you can start thinking how these nouns are related. Make sentences out of it for example:
Customers rent DVD's
Employees get commissions
Once you have come up with all possible relationships begin putting an ER diagram together. An Entity Relationship Diagram is a necessity for designing the database. The ER diagram essentially is the sketch of the structure of your database. In this case an Entity would be the nouns in your list. Those Entitys/Nouns become the tables in your database. The sentences that describe the relationship between the nouns become the relationships between the Entities.
To generate the attributes/columns of each table simply think about the noun and make a list of words that describe the noun. For examples:
What does a dvd have:
These can become attributes of that entity.
The process is much more involved as this was just a simple and quick example. The best way is to read through some tutorials or buy a good book on database design. Here are some links:
There are many tutorials available so just do a search on