When you are about to introduce your students to this second type of irregularity which some verbs manifest in the present indicative, it is a good idea to review the regular forms, then the previously learned irregularity. Usually the e>ie and o>ue are taught first, but if the e>i ones are taught first, then it is a good idea to read the warm-up or review exercise I suggested in Part 1.
In any event, elicit as much and as many answers that reveal that there is some meta-cognitive thinking going on; that is, that students know what they are doing and what the various part of a verb are and what they do. These include such concepts as knowing what a stem (or root) of a verb is, what a theme vowel is, what infinitives are and how to recognize them, what conjugation is, and so forth. Briefly review the e>ie and o>ue verbs (pensar and poder were the models I suggested in Part 1).
Do as much review as possible orally, only writing on the board to summarize, and conclude by getting them to see and artciulate the patterns. Pushing students to articulate what they see does a number of things -- it keeps them awake and on their toes, it gets them actively involved in their own learning, thus getting rid of the passive doldrums.
By teaching the various types of irregularities which manifest themselves in the present indicative in separate lessons, and quizzing before moving on to the next, you can gauge their readiness as well as what types of errors threaten to fossilize. This gives you anotther chance, during review, to short-circuit bad habits.
The e>i irregularity also occurs in the shoe pattern, but this type of irregularity as well as the consonant irregularities, will resurface when they are introduced to formal commands (one of the functions of the present subjunctive). For this reason, it is very important to tell them that whether they now learn or don't learn these patterns, and which verbs do what, will determine whether their grammatical chickens will come home to roost before the end of the year.
The best model verbs for teaching this irregular pattern are pedir and servir. Do not use decir, because it also has a consonant irregularity and the e>i one. Leave that conversation for another day.
Finally, if possible, be sure to review and get them to summarize all the conjugation patterns learned thus far, starting with regular verbs. Do verb drills.
Keep the class fast paced and their answers randomized by using synoptic verb drills.