Most of the trends we talked about for raising boiling points hold true for melting points for most of the same reasons. There is one major exception, though. The more branched, and therefore compact, a molecule is, the higher its melting point, because, in general, compact molecules will pack better in a crystal lattice. The better packed a lattice is, the more stable it is, and the more heat (energy) it takes to break up that lattice and melt the solid.