The latex and emtex drivers allow two options.
Syntax:
set terminal latex | emtex {courier | roman} {<fontsize>}
fontsize may be any size you specify. The default is 10-point Roman.
Unless your driver is capable of building fonts at any size (e.g. dvips), stick to the standard 10, 11 and 12 point sizes.
METAFONT users beware: METAFONT does not like odd sizes.
All drivers for LaTeX offer a special way of controlling text positioning: If any text string begins with '{', you also need to include a '}' at the end of the text, and the whole text will be centered both horizontally and vertically by LaTeX. --- If the text string begins with '[', you need to continue it with: a position specification (up to two out of t,b,l,r), ']{', the text itself, and finally, '}'. The text itself may be anything LaTeX can typeset as an LR-box. \rule{}{}'s may help for best positioning.
Examples: About label positioning: Use gnuplot defaults (mostly sensible, but sometimes not really best):
set title '\LaTeX\ -- $ \gamma $'
Force centering both horizontally and vertically:
set label '{\LaTeX\ -- $ \gamma $}' at 0,0
Specify own positioning (top here):
set xlabel '[t]{\LaTeX\ -- $ \gamma $}'
The other label -- account for long ticlabels:
set ylabel '[r]{\LaTeX\ -- $ \gamma $\rule{7mm}{0pt}'