Parsing Table columns?

Hi,
I have just installed Derby into my Java stand alone application. I have a table design question.

Lets say I have a table that consist of a primary key and 26 columns [A, B, ,,,Z].

With SQL statements I can select individual columns into a result-set and judicially insert new rows or replace the values in selected row / cols.

Question:
Are there any guideline articles or books that will help me in designing my tables?

For example, for the above table, I may do the majority of the run-time processing on columns A, B and C. Should I place the primary key and columns A, B and C in an individual table and maintain a second table with the primary key and columns D ... Z. Or am I over thinking this too much.

Note that my Java stand alone application is form centric and I think the Derby  access time is not all that critical since there will be a lot of data entry processing that will mask any SQL time inefficiencies.

As you can perhaps tell, I am new to Database implementation and want to do this initial design properly.