Whether one follows the Ari z"l and does not take a haircut throughout the 'Omer till 'Ereb (the eve of) Shabu'oth, or one follows one of the different opinions, a man should get a haircut on the eve of Shabu'oth prior to the Festival.
There is a special Leshem Yihud prayer which can be found in Sefer Leshon Hakhamim, which is good to say before taking the haircut. It mentions, among other things, that one should have the intent to be fulfilling the two commandments of Peoth of one's hair, one for the right side and one for the left. One should also have in mind the five Miswoth which are connected with the five corners of the beard.
There is a portion that refers to using a razor. This obviously applies to the portions of the hair where it is permitted and not to where it is forbidden. It would seem appropriate, that if a razor is not being used, that the portion should be omitted.
We are quoting it here in Hebrew for ease of reference.
(See Leshon Hakhamim 1:58)
Hair cuts before Shavuot, Shabu'oth, Shabu'ot. Using a razor on the hair, Halacha