One of the key requirements for spiritual development is being open-minded.  A close-minded person might have his path right in front of him, but will ignore it.  So before any real spiritual development, you need to become open-minded.  Of course, close-minded people probably are not reading this so those who are may have to pass on these hints to their close-minded friends.  Some simple things you can do to help open a closed mind:

1) Go shopping in a store you've never been in, especially a specialty shop with a specialty you are not really interested in.  See what kind of people shop there.  The answer may surprise you!  Some examples:
    A. If you would never change a headlight in your car yourself, go to a car parts store and look around
    B. If you think new age is goofy, go to a crystal store or some other type of new age shop
    C. If you think all Bible-thumping Jesus freaks are the same, go to Christian book store
    D. If the idea of shopping for lingerie for your wife/girl repels you, go to Victoria's Secret.

One of my most interesting shopping trips was to a Harley-Davidson Accessories shop in Reno, Nevada.  It features leather jackets, clothes, and other accessories for motorcycle fans.  I found only a small percentage of the shoppers I say there were the Hell's Angels type I expected.

2) Make friends with someone from a different background.  Another country, religion, language.  Or attend a meeting for such people.

3) Attend a church you've never been to before.  Some years ago I took a bus trip through Italy.  Even though I'm not Catholic, I did take the tour of the Vatican.  It was fascinating.  A lot of history and great art there.

4) Take a vacation to a place you've never been to, preferably, someplace a little different from you usual vacation.

5) Use a blog searching or indexing service to find blogs about subjects you think don't interest you and read some entries. 

I could probably come up with a dozen other things, but I think that is enough for starters.