It is easy to learn the first open chords and begin playing songs like "knocking on heavens door" but it is quite a lot harder to strum it correctly. To become decent at strumming one has to have a lot of strumming patterns down cold, and techniques like palm muting become important.
The basic strumming technique, whether using a pick or not, is done with a stiff wrist, where your strumming hand moves like a pendulum across the strings. The strumming pattern is created by alternating between hitting and not hitting strings when your hand is on its way up or down.
Strumming patterns are typically notated with and up/down arrows indicating which way your hand should hit the strings, but sometimes a d/u and / for break is used instead. Usually, these notations only serve as a guideline and do not tell time, so you would still have to listen to the song you want to play to get it right.
Here are some strumming patterns I've come across:
N.B. There are several other possible suitable patterns. The suggested one sometimes are not always the exact ones palyed on original recording, but in some cases are the simplest. Regarding bpm they are approximated since I did play most of the songs only along the original recording
song - original recording - resolution - Suggested pattern - Other possible patterns - approx bpm
horse w/no name shuffle B/du/B/d d/du/u/du or also du/du/du/du 110-120
knocking on heavensâ€™ door sixteen bb/ddu/bb/ddu D/du u/D/du u 70
tangled up in blue sixteen dd/ddu/ud/ddu bb/ddu/bb/ddu or D/d..u/ud/du 95-100
if not for you eight d/du/d/d/d/du/d/du (2 measures pattern) d/du/d/du 110
blowin in the wind sixteen bb/dudu/bb/dudu bb/ddu/dud/ddu 80-85
tambourine man (Byrds) eight du/du/u/du d/du/u/du 120
tambourine man (Dylan) sixteen bb/ddu/dub/ddu bb/ddu/bb/ddu
summer of 69 eight d/du/u/du dd/dd/dd/dd 125
heaven sixteen bb/ddu/bb/ddu d/du u/d/du u 75-80
back to you eight with anticipatated chord changes d/d/du/du/u/d/du/du d/d/du/u/u/d/du/du 120
feelin alright sixteen bb/d..u/ud/ddu bb/ddu/bb/ddu 100
three marlenas eight with anticipatated chord changes d/d/du/du/u/d/udu (2 measures) d/d/du/du 110
margaritaville eight b/du/B/du b/du/u/du 105-110
happy x mas eight b/du/du (3/4!!!) b/d/d 100?
imagine eight with some sixteen dd/dd/dd/dd bb/ddu/bb/ddu 75
stand by me (ben e. king) eight d/u/du/d d/du/u/du 110
stand by me (john lennon) eight dd/dd/dd/dd
riders on the storm eight du/du/u/du du/du/u/d 110
love the one youâ€™re in sixteen ddu/uu/ddu/ddu dd/ddu/dd/ddu 95-100
shot the sheriff sixteen bdu/bd/bdu/bd bb/ddu/bb/ddu 95-100
no woman no cry sixteen bb/ddu/bb/ddu bb/ddu/dub/ddu 80
heart of gold (intro) eight b/dd/dd/dd 85
heart of gold (verse) sixteen bb/ddu/bb/ddu bb/ddu/dub/ddu 85
alabama sixteen bb/ddu/bb/ddu 80-85
out on the weekend sixteen bb/ddu/bb/ddu bb/ddu/dub/ddu 75-80
one sixteen dd/ddu/ud/ddu d/ddu/ud/ddu 85
sitting on the dock of the bay eight with anticipatated chord changes b/d/du/du b/du/u/du 100
wish you were here sixteen D/du u/dud/dudu bb/ddu/bb/ddu 65
hurt (johnny cash) eight dd/dd/dd/dd 70-75
folsom prison blues shuffle b/du/b/du 110
eleanor rigby eight dd/dd/dd/dd d/du/u/du 120-130
leaving on a jet plane eight d/du/u/du 90-100
brown eyed girl eight d/du/u/du 120?
wild world sixteen bb/ddu/bb/ddu bb/ddu/dub/ddu 75-80
father and son sixteen D/ddu/D/ddu bb/ddu/dub/ddu 75-80
country roads sixteen bd/dudu 110-120
let it bleed eight d/du/u/du 120
dead flowers eight d/du/u/du 120
Iâ€™m free eight d/du/u/du 120
honky tonk woman eight d/du/u/du 120
mother little helper eight bu/du/bu/du b/du/u/du 130?
sweet virginia shuffle du/du/du/du b/du/du 120-130
spider and a fly shuffle du/du/du/du b/du/du 120-130
little baby shuffle du/du/du/du b/du/du 120-130
wild horses sixteen d/d..u/ud/ddu bb/ddu/dub/ddu 75-80
angie sixteen bb/ddu/bb/ddu bb/ddu/dub/ddu 75-80
sister morphine sixteen bb/ddu/bb/ddu bb/ddu/dub/ddu 75-80
shine on you sixteen bb/ddu/bb/ddu bb/ddu/dub/ddu 75-80
you canâ€™t always get what you want sixteen bb/ddu/bb/ddu bb/ddu/dub/ddu 75-80
like a rolling stone sixteen dd/ddu/dd/ddu bb/ddu/dub/ddu 95-100
love in vain eight b/d/d (3/4!!!!) 75
lucky man eight b/d/d (3/4!!!!) b/du/du (3/4!!!) 70
journeyman (iron maiden) eight d/u/du (3/4!!!)
nothing else matters eight b/d/d (3/4!!!!) b/du/du (3/4!!!) 70
unforgiven sixteen dd/ddu/dd/ddu bb/ddu/dub/ddu 95-100
where did you sleep that night (nirvana) eight d/u/du (3/4!!!) b/du/du (3/4)
man who sold the world eight d/du/u/du 100
pennyroyal tea eight d/du/u/du 70-75
come as you are eight d/du/du/du/du/u/du (2 measures) 100-110?
about a girl (verse) eight d/du/du/du
about a girl (chorus) eight d/du/du/du/du/u/du (2 measures)
polly eight d/du/du/du
proud may (creedence) eight d/du/u/du
have you ever seen the rain eight d/du/u/du
whoâ€™ll stop the rain eight d/du/u/du
up around the bend eight d/du/u/du
heard it through the grapevine eight with anticipatated chord changes b/d/du/du b/du/u/du 100
travellin band eight d/d/du/du 160
molina eight d/d/du/du 160
suzie q eight d/du/u/du 120
lodi eight d/du/u/du 120
green river eight d/du/u/du 120
born on the bayou eight d/du/u/du 120
looking out my back door eight bu/du/bu/du b/du/u/du 130?
long as I can see the light sixteen bb/ddu/bb/ddu 75
johnny be goode eight du/du/du/du 165
wanted dead or alive sixteen d/d..u/ud/ddu dd/ddu/ud/ddu 75
every rose has its thorn sixteen d/d..u/ud/ddu dd/ddu/ud/ddu 75
I remember you sixteen d..u/ddu/ud/ddu dd/ddu/ud/ddu 80
forever (kiss) sixteen dd/ddu/dd/ddu 85-90
goin blind (kiss) sixteen dd/ddu/dd/ddu dd/ddu/uu/dudu 80
patience eight d/du/u/du 90-100?
sweet child o mine eight d/du/u/du d/du/u/d 120-130
take it easy eight d/du/u/du d/du/u/d 120-130
peaceful easy feeling eight d/du/u/du d/du/u/d 120-130
tequila sunrise eight d/du/u/du d/du/u/d 100
already gone eight d/du/u/du d/du/u/d 130
lyin eyes eight d/du/u/du d/du/u/d 110
hotel california sixteen dd/ddu/dd/ddu dd/ddu/uu/dudu 80
desperado sixteen dd/ddu/dd/ddu 70-75
after the thrill is gone sixteen d/d..u/ud/ddu dd/ddu/ud/ddu 70-75
new kid in town eight d/du/u/du 100-110
lady in black sixteen dd/ddu/dd/ddu 80-90
sunrise sixteen dd/ddu/dd/ddu 85
stealin shuffle du/du/du/du 130
wizard sixteen d/d..u/ud/ddu dd/ddu/ud/ddu 75-80
tales sixteen d/dud/du u/dd 75-80
rain eight d/du/u/du
easy livin shuffle du/du/du/du 180
no need for me to type it up again when others have said it better than I ever could:
Strumming with a pick:
A lot of beginners have problems strumming with a pick because they hold it at an angle which lets it glide across the strings downwards, but catches if they try an upstroke. So they try altering the angle for upstrokes, which means rotating the wrist all the time between strokes - very unnatural and awkward.
In fact, the best method is to hold the pick at 90Â° to the strings for up and downstrokes. Ideally use a thin, bendy pick, and grip it tightly, with plenty of point showing. The pick will give as it passes over the strings - and if the angle is right, it will work in both directions. If you only have a medium or thick pick. hold it loosely and let it give as you strum. Try and keep your wrist angle the same, both up and down.
Strumming with fingers:
If your nails are long, best method (IMO) is to use the backs of your fingernails for downstrokes, and back of the thumbnail for upstrokes.
Alternatively the thumb will do for both strokes, but hold it. Experiment with different angles, but you should find something that works without too much difficulty.
Strumming with a pick is generally better, because it gives a cleaner, more precise sound, and more dynamic range (you can strum pretty quietly with a pick if you do it right).
Fingers (even with nails) give a softer, more vague sound - and if you do it too much you can wear down your nails, which is a problem if you want to use them for fingerpicking.
With all strumming methods, pivot mainly from the elbow. The forearm should move like a metronome: down on the beats, up between the beats - whether you hit the strings on each stroke or not. You don't change your arm movement for different strumming patterns - you just vary which passes of your hand (up or down) make contact with the strings.
(Watch as many rhythm players as you can. You rarely see their arms move in a complicated way, even on complex, syncopated patterns. They may shorten the stroke sometimes, but they rarely change direction, ie, to play upstrokes on the beat.)
It's a little more complicated for rhythm patterns that use 16th notes (eg "Smells Like Teen Spirit" or "Wonderwall" - then the downward movement tends to be on every 8th note; but the main 1/4 note beats are still the most forceful downward moves.
With upstrokes (even with some downstrokes), you rarely need to hit all the strings - frequently upstrokes only contact the top 3 or 4 strings, and this is fine. Rhythm guitar is more about percussive, rhythmic feel than full chords for the harmony.