Watch the Steal From The Best online guitar lesson by Matthieu Brandt from Songwriting on Guitar
A great way to enhance your songwriting toolbox is to study the elements your favorite writers have used. Song structures, guitar tricks, rhythmical forms, melodic phrases, etc.. Try to define what you like about a certain composition.
A great way to get a solid grib on these elements is to write a song 'modelled' after the composition you like. Change the chords around, alter the melody, put your own lyrics on top, but keep whatever you dig about the song.
The more you think in abstract terms about these favorite songs and the compositional elements they use, the quicker you'll be able incorporate these parts into your song.