You can print out a composition in the form of a musical score, using the -> function or the -> function.
Producing a score from performance data is a hard task, and in most cases it's unreasonable to expect a default printout based on MIDI data to be very readable. You should use the notation editor to tidy up the score before printing. (See also Notation from performance data.)
Rosegarden is capable of producing very readable scores. Even so, it is designed to be a screen editor and not primarily a typesetter. If you want to produce true print-quality scores you should consider using LilyPond in conjunction with Rosegarden. LilyPond is music typesetting software that reads a specialised text file format and produces high-quality typeset output. Rosegarden is capable of writing LilyPond files using the ->-> function, and it features special exportable directives and track parameters that provide access to LilyPond features for which there is currently no parallel within Rosegarden's own native interface.
LilyPond may be conveniently used with the -> function, which exports the file into a temporary file and processes it directly with LilyPond for preview with a PDF viewer. If you are happy with the preview, you may print the score using the printing capability of the PDF viewer, or use the -> function.
When Export, Preview, or Printing is done with LilyPond, there is available also a collection of LilyPond options.