Another thing I did with Spanish and Italian was that I allowed the similarities to help me, and I focused hard on the differences. When studying, I would pay most attention to the things that were different in Italian than they were in Spanish, and I'd connect that in my mind to the Spanish word. So if I couldn't remember something on an Italian test, I'd think, "What is this in Spanish?" and from there I'd try to connect the next dot to the Italian word.

The last thing I'll say here is that it's not easy, and sometimes in ways you don't expect. During finals of the semester where I took Spanish, Italian, and Korean all at the same time, I had a nightmare one night in which I was trying to take my Italian final using the Korean alphabet while my Spanish teacher criticized my work, haha.

Amy wrote:

I had a nightmare one night in which I was trying to take my Italian final using the Korean alphabet while my Spanish teacher criticized my work, haha.

That was a really good laugh Amy! 

I just started a project where I will be learning 10 languages at the same time (very slowly). Insane right? I wonder what kind of nightmares I'm going to have. :P

I can't give you any advice on how to avoid confusing those two in particular, since I've never studied either one.  But I can tell you what I did (and what I wish I would have done differently) when I studied Spanish, Italian, and Korean all at the same time, and what I do now, while I'm studying just Spanish and Korean at the same time (though obviously the Spanish/Korean combo doesn't conflict much, unlike Chinese/Japanese or Spanish/Italian).

The thing that helps me the most is to avoid switching rapidly between the two (or more) languages.  It's especially important for me not to switch from the language I know better to the language I know less.  So, I don't study Spanish right before Korean class, and I usually don't study Spanish right after Korean class either (though it's not such a big problem if I do).  I took Italian for only one semester (this past fall), after studying Spanish since 5th grade, and unfortunately I had Italian immediately after Spanish, which was a disaster.  It did help when I came in on the first day of class and the teacher spoke entirely in Italian the entire period - my brain was still in Spanish mode, so I just interpreted everything he said as being butchered Spanish and understood most of what he said.  But every day after that, I found myself making mistakes in my work that were caused by my confusion between Spanish and Italian.

Every pupil at fifteen in my country learns three languages, it is no problem. Why should it be a problem?

I am from China and I'm learning Japanese. I think the only thing the two languages have in common is kanji. So I don't think it is likely for the two languages to confuse you.