Before class, type out ten or so sentences in Spanish that use either an indirect or direct object pronoun. Between all your sentences you should have one example of each of the pronouns so students can practice all the different forms. In your sentences you will want to use verbs and nouns that the students have already had. You want most of the challenge to come from deciding which pronoun to use. Use a larger font when typing these sentences out and leave a large space between the words and the sentences. Cut out each word from all of the different sentences and keep a list of the original non cut version to work with. Place the words in an envelope and repeat this step ten times so you have ten envelopes in all.
Now, split the class into groups of fours. Pass out one envelope per group and tell the class to spread out the different Spanish words. Students should categorize the words into verbs, nouns, pronouns, articles and adjectives. Since the words for all ten sentences will be in this pile it may take a little while for them to categorize them correctly. Walk around the class and help out with any questions / problems.
Once the groups have their words in the correct categories explain to the class that you are going to read a sentence in English out loud. Each group is to form this sentence in Spanish using the words spread out on the desk. Working as a team, students will discuss how the sentence should be written. Explain that each sentence will have a Spanish direct or indirect object pronoun in it. Circulate around the room and give hints to struggling groups. Once a team believes that they have the correct answer they are to raise their hand. You will now check the answer and give points if a word or two is off.
Have the groups continue with the first sentence until all groups have formed the sentence correctly. At this point tell the students to put their words back in the correct categories and you will now start with the second sentence. You may want to write the English version of the sentence on the board so you do not have to keep repeating it. When you have finished a round you can go over the grammar of the sentence and discuss why a certain pronoun is used. Keeping score can sometimes be fun and used as extra motivation.
Everyone will work hard on this and will really participate as a team to come up with the correct Spanish sentences. Save the materials for future use. Good luck!