It's just "be ready (infinitive)", as in, "let's get ready to go", or "let's get ready to eat", or "I am ready to leave", or even "be ready to go in five minutes" which would be a command.

I think the difference is that for 'be ready for doing something' the emphasis is on the verb. eg: I'm ready for going skating. I'm ready for doing some study now. If you say 'be ready for something' the emphasis is on the noun. eg: I'm ready for the party. I'm ready for the wedding now. etc.

be ready for doing 是 be ready for sth 中的一种特别形式。这里的do是代指动词。所以doing的意思实际上是 v.+ing。而动词v.加ing就是名词。比如，动词read，读，加ing就是名词reading，阅读。walk，走；walking，散步。 所以以上两种都是对的 ，可以这么写 be ready for sth（doing/v.+ing ，n.）

As soon as you find they are actually exactly the same, you'll get over the grammar barriers.