(These rules apply to direct object, indirect object and reflexive pronouns, and 'y' and 'en'.)

There are three important rules.

1)  Pronouns always go just before the verb which they complement.

          Quand mon copain me donne des chocolats, je les mange tout de suite.
          (When my boyfriend gives me chocolates, I eat them right away.)

     If there are modal verbs, they still go just before the verb which they complement.

J'aime les manger très vite, sans les sucer.
(I like to eat them very quickly, without sucking them.)

('les' (chocolats) are the object of 'manger', not 'aime')

Je devrais les manger plus lentement, mais je ne peux pas m'empêcher de les manger très vite.
(I should eat them more slowly, but I can't hold myself back from eating them very quickly.)

2)     In compound tenses, pronouns go just before the auxiliary.

J'ai vu un autre film de Cédric Klapisch, et je l'ai beaucoup aimé aussi.
(I've seen another film by Cédric Klapisch, and I liked it a lot, too.)

Je lui ai donné quatre étoiles dans ma revue.
(I gave it four stars in my review.)

3)     In negative sentences, pronouns always follow the 'ne'.

Je n'aime pas les films de Jean-Luc Godard, par contre, parce que je ne les comprends pas.
(I don't like films by Jean-Luc Godard, though, because I can't understand them.)

So in negative compound tenses, pronouns will go between the 'ne' and the auxiliary.

J'ai vu son film Week-end, et je ne l'ai pas aimé.
(I've seen his film Weekend, and I didn't like it.)

 

There are also three more difficult rules that are less important.

4)     In affirmative imperative sentences, pronouns go after the verb, and are linked         to the verb with hyphens.

Vois-le, si tu veux.
(See it, if you like.)

Donne-lui toute ton attention.
(Give it all your attention.)

5)      In negative imperative sentences, pronouns follow their normal order, before          the verb.

Mais ne me dis pas que je ne t'ai pas averti.
(But don't tell me I didn't warn you.)

6)      If you have more than one pronoun in the same clause, they will follow this          order:

me
te
se
nous
vous

le
la
les

lui
leur
y
en

         It doesn't matter if a 'me', 'te', 'nous' or 'vous' is a reflexive pronoun, a direct          object pronoun or an indirect object pronoun, it will always come first.

Tu as vu tous ses films? Il y en a beaucoup.
(Have you seen all his films? There are lots of them.)

Ne m'en parle pas.
(Don't speak to me about it.)