If you want to get into jazz you are going to have to learn to read a chart. You might be able to get away with not learning to read notes if you have a good ear and can find melodies easily, but when it comes to form and understanding a tune you really need to understand what's on the page!

Things to watch out for

Feel or Style
Is there any indication written for the feel or style, like Swing, Bossa, Bop or any other clues as to how you should approach the tune?

Time Signature
Check the time signature forst off so you know how many beats in a bar. If nothing is written you can probably assume it's in 4:4.

Tempo
Some charts have the tempo (speed) marked, some don't. Have a look and see.

Key
Look at the Key Signature. If you don't understand the term, go check out Practical Music Theory. You need to know the key to communicate with other musicians what key you want to play a tune in. Also check for Key Signature changes during the tune.

Repeats
Next scan the overall form of the tune, particularly the repeats and where they go back to. The repeats are a thick like a thin line and two dots you will go 'where the eyes look' :)

% Repeats
The symbol that looks a lot like a percentage sign means repeat the last bar.

1st and 2nd time bars
You'll sometimes see alternate ending shown with a 1˚ (1st time) and 2˚ time shown. There will be a repeat at the end of the 1˚ area and the second time you come to that point you skip the 1˚ section (think that the door only lets you in the 1st time!) and go to the 2˚. Some complex songs may have even more alternate endings to sections but it;s unusual.

D.S al Coda.
You will find this written sometimes at the end of a tune. You will go back to the D.S (I call it Da Squiggle) and then play until you reach the Coda (which looks like a gun sight) at which point you'll jump to the coda section which will usually be written after the end of the main song sheet music. Variation is D.C al Coda which means go back to the start until the Coda.

Coda
Sometime you'll see a Coda in a chart but with no directions like D.S or D.C, you can assume you will only take the Coda when you want to end the song, so it will be to "cue" and you'll have to keep an eye on the rest of bands eyebrows!

[A] [B] and [C] Sections
Make sure you note the sections if they are maked, they're used for rehearsals where your band might need to work on a particular bit, and in some songs (like Green Dolphin Street) you might have feel or time changes betweene sections!

X3
Also watch out for the old 'Times 3' (X3) or any similar variation, can throw you into a Train Wreck if you miss one!!

Pause
A dot with an arc over it (like a rainbow!) means to pause on the note or chord below it, so it takes you out of tempo and you'll have to follow by eyebrow ;)

Two Staves
Just for those that are not used to reading dots, if you see two staves (two sets of lines) with a backwards C: in the bottom stave, it's probably written out for piano. You can still read the chord fine though! It's not always the case though as some charts might have alternate melody lines or other crazy stuff, you have to research a tune a bit when you see a strange chart - remember that some of the Real Book charts are wrong and plain badly written... while others are excellent!

Songs or artists written at the bottom of the chart
You will often see versions of the songs written on the bottom of a Real Book Standard - check them out, they are likely to be the version that the guy who wrote the chart was listening to, so it's probably good :)