When making images and perspective views of large amounts of data, the GMT programs can take some time to run, the resulting PostScript files can be very large, and the time to display the plot can be long. Fine tuning a plot script can take lots of trial and error. We recommend using grdsample to make a low resolution version of the data files you are plotting, and practice with that, so it is faster; when the script is perfect, use the full-resolution data files. We often begin building a script using only psbasemap or pscoast to get the various plots oriented correctly on the page; once this works we replace the psbasemap calls with the actually desired GMT programs.
If you want to make color shaded relief images and you haven't had much experience with it, here is a good first cut at the problem: Set your COLOR_MODEL to HSV using gmtset. Use makecpt or grd2cpt to make a continuous color palette spanning the range of your data. Use the -Nt option on grdgradient. Try the result, and then play with the tuning of the .gmtdefaults4, the cpt file, and the gradient file.