You have to start somewhere.
This page helps to explain about the varying difficulty of songs to parody. It is divided into two main parts - the factors that affect the difficulty, and how I rank difficulty.
The things that affect the difficulty of a song are a few main things - amount of lyrics, how complicated the words are, the clarity of the subject - where you ideally want to be somewhere in the middle of the range. I liken these to teeter-totters that you want to have balanced. Like many things in life, each of the following things to take into account has two similarly bad extremes, even if one extreme is not as obvious a problem as the other.
This is always a trade-off. A song with a lot of lyrics gives you more to work with, but a song with few lyrics is easier to memorize.
An important consideration is that every lyric of your parody can affect other lyrics, as they all need to make sense together. At first you should stick to songs with limited lyrics, as doing so makes the chain reaction easier to deal with. Once you are an acquainted parodist, however, you will learn to appreciate having more space to tell a story, so in the long run, it is better for a song to have too many words than not enough. The likes of A.D. 1928 and A.D. 1958 will never be good choices, but a song with enough lyrics for multiple ordinary songs might be an excellent choice, but for experts only. I do put emphasis on might be,
however (as you can see from the last section of the poor fodder example).
Polysyllabic words tend to make a song more difficult. For more information on them, see my advice on how to deal with them.
Often, whether or not the song title contains any polysyllabic words is your first clue to how difficult it is. This is not an absolute guide, however, since the general vocabulary is sometimes different from what the title suggests, especially because, while the title of a song usually does appear in it, it is not guaranteed. Green Day have a history of songs whose titles are not actually in the lyrics, especially in their earlier albums. Sassafras Roots is a good example of a song of theirs that is less than meets the eye.
Then again, having words with specific meanings can be helpful for figuring out what you should make the song about. If all the lyrics are written in generic, broadly applicable terms, you may find yourself having no hooks to get ideas from. The Loverboy song It Don’t Matter, described in the behind-the-scenes section of my page for their first album, is a good example of a song that is actually too flexible to be suitable for parodying.
It helps if it is easy to understand what a song is supposed to be about. If you cannot figure that out, the song will seem to you like it is about nothing, which means it will remind you of nothing, which means it will give you no ideas. On the other hand, a song that leaves too little to the imagination will have too few blanks for you to fill.
I have come up with difficulty ratings to give albums:
This rating is synonymous with songs that can be memorized in few listenings, have easy words to rhyme, and generally tell clear-cut stories. These albums are often among the earlier works by their artists, and are likewise ideal for parodists in training.
Mostly simple albums are similar to easy albums, but are slightly more prone to featuring difficult words or murky stories. As you can see from the list of albums by difficulty, it appears to be one of the difficulties that attract me the most. I believe this is because these albums are easy enough that they pose little trouble for me, but hard enough that my readers are unlikely to think of obvious parodies I or anyone else could have come up with (a concern that this page sheds some light on).
This is as difficult as most albums get.
You know you are not dealing with a typical rock band when I put an album in this category.
This is a rare difficulty rating that I apply to only two albums I have done, Kilroy Was Here (Styx, 1983) and American Idiot (Green Day, 2004). They are two of the least conventional albums I have, both having a story running through the whole album among other uncommon things.