Hi Tom, I can understand what you said perfectly. Actually your pronunication is not bad at all. :)

Notes

我是31岁 => 我31岁 It is different from English, you do not need to add 是（is）here.

我是英文老师，在大学 => 我是大学英文老师 You can combine the two sentences

我喜欢踢足球和练习功夫和打篮球等等 => 我喜欢踢足球，练习功夫和打篮球等等。 我喜欢A,B和C。

我喜欢中国，因为中国人很有名。  有名 = yǒu míng  You need to pay attention to the pronunciation of ming. It is the second tone, not the fourth tone. 

可是学习中文是很难 => 可是学习中文很难 you do not need to add 是 here

旅游 lǚ yóu 

如果我旅游在中国，很多人听不懂我 => 如果我在中国旅游，很多人听不懂我在讲什么。will sounds more natural

I'll let the native speakers comment on your pronunciation as they're advice is much more valuable than mine.

But I thought I'd let you know that I perfectly understood what you were saying! Also, to me, your grammar/sentence structure is fine!

My  "Tips for Chinese learners's pronunciation" submitted here for your reference:

http://www.italki.com/discussion/74900

Hopefully it can help your problem, and your learning goes well.

Are you talking about tones in particular? Or the vowel/consonants (zhi, shi, chi etc)

Getting the pronunciation is always difficult when you're first starting out a new language.  But your mouth/brain gets used to forming those new sounds and adapts itself over time.  Well, that was my experience for language with lots of new weird sounds like French.

I'm sure you know the "description" of each tone (eg. 1st: high flat, 2nd: rising etc).  You should just practise them in your head the whole day (out aloud is better! I talk to myself in foreign languages when I'm in the car alone).  When you're alone, you don't feel embarrassed and you just do whatever it takes to nail the sounds.  And when you are actually talking people, you'll be surprised at how much more fluidly you can communicate.

:) 加油

Perhaps you can listening the CCTV News in each day at Beijing time 7:00, since the broadcasters pronounce standardly, so you can practice your pronunciation with it.