I came across this blog based on the advancement of adult literacy and English as a second language training. In particular I came across a posting that offers some good advice on spelling words in general. Here's what the author had to say:

1. Spelling words should be words that the student is already familiar with through speaking, listening, and reading.
2. Word lists should focus on high frequency writing vocabulary. For example, use high-use words from work reports, children’s school notes, postage and mailing, etc.
3. The spelling rules that you teach should be the ones that apply to a large number of words with few exceptions.
4. Excellent spellers use a Visual Memory strategy to learn new spelling words - taking a mental photograph of the word to put into longterm memory. Other supportive strategies include breaking up the word into pieces, derivation, rules, sound, use of the dictionary, and sound.

The article went on to provide some lists of useful spelling words:

--Level one high use spelling words
--level two high use spelling words
--level three high use spelling words
--level four high use spelling words
--level five high use spelling words