不定式的并列从第二个起要加to不？谢谢了

两种情况，当所需表达的意思为不须强调时，不用加

如你的例句：I want to look at it and do it.

当所需表达的内容是要强调的时候，应该加to（通常口语）
如：The Chinese government's heavy invest on 2008 Beijing Olympic Games is not only to enable the whole world to see that China is completely competent to hold the world biggest event, but also to show their strong position in the world.（不好意思，例句有点长）

不加
ps. I'd like to go to the shop and buy a pen.

不需要。并列的两个动作都是跟在谓语动词want to后面，两者都是想要做的事情。