比, 没有, 一样 or 最

Four patterns cover most comparisons:

• A 比 B + adjective: 哥哥比我高 (my brother is taller than me). Put the size of the difference after the adjective (高十厘米, 大三岁, 贵一点, 快多了) or 更/还 before it (比昨天更冷). Never use 很 in a 比 sentence.
• A 没有 B 那么/这么 + adjective: 我没有他那么高 (I'm not as tall as him). This is the usual way to say "not as … as".
• A 跟 B 一样 (+ adjective): 我跟姐姐一样高 (my sister and I are the same height). 和 can replace 跟.
• 最 + adjective: 她是我们班最高的学生 (she is the tallest student in our class). 最 also goes before verbs like 喜欢.

In speech 没有 is often shortened to 没, and 不像 can replace it. 不如 also works, mostly with qualities you'd want: 这本书不如那本有意思 (this book isn't as interesting as that one).