Cook couscous in a large pot of  salted, boiling water until al dente.  Drain in a colander and rinse with cold water until cool.

Segment the grapefruit and clementines by first cutting away the skin and pith, following the curve of the fruit, and then releasing the supremes by slicing on either side of the membranes.  Do this over a bowl to collect any juice, and squeeze the centre membrane to get out as much juice as possible before discarding.  (See link to tutorial in post.)  Divide citrus segments between four plates.

Whisk the olive oil, tarragon, honey, vinegar and salt into the reserved citrus juice.

Toss the couscous with a bit of the dressing, then divide among the plates.  Toss the beets with a bit of dressing and do the same. Drizzle salads with remaining dressing and some more tarragon leaves.