|METAPHOR— DO NOT TAKE LITERALLY|
Here I've put together a list of pieces of information you get from whatever piece of music someone hands you in a playing situation, in the rough order in which you process them:
Do I know this tune? Have I played or heard it before? Is this the familiar form of the tune, and I can throw the chart away, or has somebody written an arrangement that I'm going to have to actually read?
You have to just listen to a lot of records, play a lot of gigs, learn a lot of tunes— especially tunes you know people in your town are playing, which are therefore likely to come up on gigs you'll be playing.
Looking at the time signature at the top of a chart, along with the context (what kind of band is it, what other tunes have you been playing this evening?), will tell you a lot about what you're going to play. If every tune on the session has been a swing tune, it's probably going to be another swing tune.
Most of your actual job is to play time in the style of the tune. There may be a style indication on the upper left of the chart, or above the staff if there is a style change during the tune. If there is no indication on the chart, and you don't feel confident about guessing based on the meter and the context, you can ask the person who called the tune. If it's an actual arrangement with a drum part there will usually be a style indication, and the arranger will probably have sketched out a crappy drum groove, or indication of a swing beat.
4. Form / roadmap
Is it a standard form, or a modified standard form? Is it a non-standard form, meaning you'll have to follow the chart carefully all the way through? Is there a written intro apart from the normal form of the tune? If there is a D.S./D.C.? Do you take it on the head only, or also during the solos? Or only the last time through? Is there a coda? Is there a fine? Do those apply only to the ending of the tune, or every time through? Those are things that are often ambiguous on charts, and you're not stupid for asking. Is there a solo form that is different than the form on the head of the tune? Usually you can spot this on the page— it may just be simplified chords for blowing, or it may be a different form just for the solos.
5. Harmonic rhythm
Typically this means how many chords there are per measure— often one, two, or four, or one chord for multiple measures. Obviously we're not playing chord changes on the drums, but paying attention to them helps you keep from getting lost, and helps you reorient yourself when you do get lost, and it can also represent energetic changes that you want to reflect in your playing.
Use your eyes and ears, follow the chart, and pay attention to the changing color of the chord progression as you play through the tune. Notice the difference in sound when there is one chord per measure vs two or four. Mentally flag the chords that jump out to your ear— if are any special spots that sound significant, you can use that to reorient yourself if you get lost. Look and listen for that chord to happen elsewhere in the chart.
This is the first order of actual specific playing instructions you need to observe: places in the arrangement where you're supposed to stop playing time. On lead sheets they're often indicated with “N.C.” in the place of a chord symbol; on actual arrangements they're indicated by normally-written rests.
Be able to stop and start your grooves cleanly, be able to count rests, and be able to do some simple lead ins getting back into the groove.
7. Other arrangement elements
Dynamics, written bass lines, tempo changes, feel changes, fermatas. Know what these and other common notations mean. Be able to play a time feel to fits, supports, or at least doesn't clash with the a bass line in whatever rhythm.
Things the rest of the band plays that you're supposed to play along with them, and possibly set up— either with a simple setup of one or two notes, or with a fill. In big band style charts there will be section figures written above the staff which are optional/informational, and ensemble figures written inside the staff that you are definitely supposed to play.
This is actually a fairly large area of study. Learn to read syncopated rhythms, dotted rhythms and ties using mainly 8th notes and quarter notes (a la Ted Reed's Syncopation), as well as 16th note rhythms, 8th note triplets and quarter note triplets (see Louis Bellson's Reading Text in 4/4 or The New Breed)— to a lesser extent. Learn to set up syncopated kicks with one or two notes on the snare drum or bass drum, or a combination of the two, with or without extra embellishments. Be able to fill in a way people can follow, ending cleanly on any beat. Good books for working on this are Studio and Big Band Drumming by Steve Houghton, and Drum Set Reading by Ron Fink.
9. Melody line
The actual written melody of the tune. This may be very important— with a tune like Evidence, on which the drummer usually plays the entire melody rhythm on the drums— or fairly inconsequential—many standards don't have a strong rhythmic element, and are often played loosely by the lead instrument, in which case you just play time. Usually you do something in between, catching a few salient points in the melody line (often tied notes, other long notes landing on an &, isolated notes, or other obvious accented notes), and possibly filling in the spaces in the melody with comping or actual fills.
10. Drum notation
The last thing I ever want to read in a piece of music is an exact drum part. If a chart has actual drum notation in it, you can usually consider it to be a loose suggestion, or an example of the type of thing the arranger wants— you don't have to play exact grooves and fills. You may use the written drum part to inform the way you play the style; if it says “LATIN” at the top of the page, and the arranger has written out a kind of mambo beat, you wouldn't play a samba. On a funk chart you may pay attention to the bass drum rhythm, which may be intended to line up with the rest of the rhythm section. Often you can tell from the way they've sketched out the swing beat whether you're supposed to play in 2 or in 4.