For more professionally looking tables you probably want to try booktabs package. The tables produced with this style look more like the tables you can see in the books, scientific articles, and newspapers. The tables differ from the plain LaTeX tables in a few aspects:
You can choose the table style in the output options under the result. If you select the booktabs style, both top and bottom rules will be added automatically.
A column is as wide as its longest text. To wrap its text, give the column a
width: drag the right edge of its header above the table, or right-click the
header and choose Set column width (double-click the edge to
make the column as wide as its text again). It becomes a p{}
column of that width. To make the table as wide as the text on the page,
choose Width: Wrap to text width in the output options: the
columns with a width share what the other columns leave of it (a
tabularx table). Scaling the table to the text width shrinks its
text too, which most style guides advise against.