>Blood (260000 results) or 血液 (3000 results)?
well, 血 gives 222 937 results but now I noticed that pixiv uses both English and Japanese synonyms to do searching so probably there is no difference in some situations.

When choosing tag I try to type it into search box and looks for suggestions.
pixiv automatically gives japanese versions so you can choose which is best.

pixiv allows to use 10 tags and you probably should fill as many as possible