Students with different levels have different problems in using "measure words", beginner always forget to put such word before noun, intermediate students usually put wrong word, and the advanced students more likely forget noun.

          What is "measure words" and why they are so important?

        量词（liàng cí）, classifier, are widely used in Chinese language. In most situation, you can not just say "how many" + "what", like three books in English, but "how many"+"classifier+"what", 三本书（sān běn shū ）. If you feel that's hard, try thinking of English when you want to say "three bags of books" or "two cups of tea". It's the same story in Chinese, the difference is almost all the nouns need classifier, except most of the time words: 天（tiān, day）、年（nián, year）、分钟（fēn zhōng, minute）、小时（xiǎo shí, hour） etc.

           Since classifier is not new for you, the only problem is how to pick up the correct one.

1. For human:  个gè、位wèi、名míng
            个gè is very common used classifier. It can be used not only for human, but article, animal, mood, theory and so on. 个gè may often (but not always) be used in place of other classifiers; in informal and spoken language, native speakers tend to use this classifier far more than any other, even though they know which classifier is "correct" when asked. 九jiǔ个gè人rén（nine people），八bā个gè 学生xué sheng(eight students)……

            When refer to human,  个 gè doesn't show any respect, which means you can not use it for anyone respectable, like teacher, expert, artist, high rank official or leader. In this case, you have to choose 位, for example: 四sì位wèi老师*lǎo shī(four teachers) 、一yí位wèi专家zhuān jiā (one expert)、这zhè位wèi艺术家 yì shù jiā(this artist)、两liǎng位wèi歌唱家 gē chàng jiā (two singers)、十 shí位wèi领导 lǐng dǎo (ten leaders)……

            名míng is a formal word, not showing any appraise. 三sān名míng学生xué sheng、五wǔ名míng教师* jiào shī (five teachers) ……
*Aware the different "teacher" here.

             2. For animals: 个gè、只zhǐ、头tóu、条tiáo、匹pǐ （for horse only）、尾wěi（for fish only）

            只 is used among small and median size animals usually, like rat, cat, dog, bird, monkey: 三sān只zhǐ小猪xiǎo zhū (three piglets)、五wǔ只zhǐ老猫 lǎo māo (five old cats)、一yì只zhǐ大黄狗dà huáng  gǒu (one big yellow dog)、一yì只zhǐ灰老鼠huī lǎo shǔ (a gray rat/mouse)。

            头tóu for big animals, but pig can be big too : 一yì头tóu老母猪lǎo mǔ zhū (one old sow)、十八 shí bā头tóu大象dà xiàng (eighteen elephants)、四sì头tóu牛niú (four cows)、五wǔ头tóu老虎lǎo hǔ (five tigers)……

            条 tiáo for animal has long body but no legs or has very short legs: 四sì条tiáo蛇shé (four snakes)、八条tiáo鱼yú (eight fish)、二十èr shí条tiáo毛毛虫 máo máo chóng (twenty caterpillars)……

             3. For plants: 棵kē、朵duǒ（flower only）、片piàn（leave only）、颗kē、粒lì、条lì
 
           棵kē is used with tree, young plant, grass. 一yì棵kē大树dà shù (one big tree)、五wǔ棵kē苗miáo (five young plants)、无数wú shù棵kē小草xiǎo cǎo (countless grass)……

            颗kē for tiny and round thing, usually seed and bean: 一yì颗kē种子zhǒng zi (one seed)、五wǔ颗kē黄豆huáng dòu (five yellow soybeans)……

            粒lì similar with 颗, also for tiny things, but most like rice, wheat: 一粒lì种子zhǒng zi 、五wǔ粒lì黄豆huáng dòu、三sān粒lì米mǐ (three grains of rice)、八bā粒lì小麦xiǎo mài (eight grains of wheat )……

            条lì for root: 五wǔ条lì根gēn (five roots)