A few people have asked me this by email, so here's the answer I gave them:
Remember, to really 'know' an HSK word you have to be able to use it in all of the different ways that Hanban expects you to. See my recent posts on HSK 1, HSK 2, and HSK 3 example sentences.
In my last post I announced some new Pleco English-English user dictionaries. Here's a guide that shows how to install these dictionaries in Pleco 3.0.

Step 1: Get the zip file into Pleco

  • Open the Web Reader in Pleco from the Navigation Pane->READER->Open Document->Web Reader.
  • Navigate to http://hskhsk.com/dictionaries (1)
  • Click on the download link. (2)
  • Click Open.  (3)
  • Click Save . (4)

I have created two English-English User dictionaries for use with Pleco. They are converted from Webster's Unabridged (1913) and WordNet 3.0 (2006). You can download them here! I also wrote a quick guide to installing them in Pleco 3.0.
As well as learning the vocabulary for each HSK level, you have to learn how to use the words in a sentence. For some words such as nouns this is pretty obvious, but some verbs and other harder to classify words can only really be learned by example. I have created files which give example sentences for HSK levels 1-3, but even if you aren't studying for the HSK they might be useful for you.

You can either browse these files to verify that you understand the usage examples or import them into a flashcard testing app. There are versions formatted for both Pleco and for Hanzi StickyStudy. The formats are simple tab-separated and it shouldn't be hard to modify them for other flashcard programs.  I mentioned this file before, but I have added English translations for level 3, and started adding my own example sentences for a few of the level 3 words where the usage isn't completely obvious.
I have uploaded new versions of the HSK 2012/2013 lists, ordered by frequency. There are links to these new lists on the word lists page. This is a pretty good ordering to learn the words in each list; from the most to least frequent. The only change to the frequency odering is when a multi-character word would be learned before the characters within that word - in that case the characters are moved in front of the word.
If you use Pleco's flashcards to study for the HSK, you should update to the latest words lists. Uploaded to the Word Lists page, and to Pleco's Forums.
This graph gives a quick way to visualise all HSK words. Words are coloured by HSK level. More common words are closer to the centre of the graph. You can download a high resolution version from this page.
I have uploaded some HSK 2012 word lists. There are versions with just simplified characters, and others with simplified, traditional, pinyin, and definitions which might be handy for anyone but are specially formatted for use with the iPhone App Hanzi StickyStudy.  There is also a list of example sentences that illustrate grammar points, taken from the HSK information published by Hanban. You can download all of the lists here.

I have uploaded a few HSK word and character graphs. See the Graphs Download page for high resolution poster-sized images  and graph files that you can use.

Most of these images are quite pretty, and some might even be useful to help learners to visualise which words share characters, etc. I am currently using the HSK 1-2 and 1-3 word charts to study for HSK levels 2 and 3.

These graphs were generated by a script that I wrote in Python. HSK word lists came from chinesetest.cn. Word frequencies, which were calculated from subtitles, are from SUBTLEX-CH. Character frequencies and composition are from distributed node weight (DNW) data. The graphs were drawn using Gephi and Graphviz. Some pinyin data came from the free Chinese dictionary CC-CEDICT.