Yes. What Cytania said. I'm not sure exactly what your strumming issues are, however many people's strumming issues result from one of two things. First, they can't get the chord change fast enough and have to break the rhythm to get to the chord. The solution for that is to do the chord changes without strumming. Sit down with your guitar in playing position. Put your hand into the shape of the letter c, gently rest the thumb onto the center of the back without changing the shape of your hand. Then when you decide go to the first chord. Strum it once. Get a good clean sound. If you've got some "mud" in there, get your fingers to the right place. When you've got a good clean chord, then go to the second one. Take as long as you need to get to the chords and get a good clean sound. That's it. Stop. Just practice that one chord transition at a time. For Am F C G, do this with Am to F. Do it about 100 times. Then do F to C. Do that about 100 times. Then do C to G. Do that about 100 times. Don't try putting any rhythm in yet. You're just trying to teach your fingers the chord shapes and how to get from one to the next. You are not trying to play a song yet. You are learning muscle memory for getting to the chords you need. After a few nights or a few weeks, all depending on how long it takes your fingers to get used to it, you'll be able to do all four chords one after the other.
When you can get a good clean sounding chord most of the time, then get a metronome. You thought I was going to say to play the song didn't you? Nope. You need a metronome. Because the second "strumming problem" many people have is that they don't understand rhythm. Note that I didn't say they don't HAVE rhythm, I said they don't understand it. You have rhythm. If you can say the Pledge of Allegiance or the ABCs song or say a phone number the same way other people do, you've got rhythm. Now you just need to understand it so you can apply it elsewhere. That's what the metronome is for. Assuming that you're doing western style music as opposed to Japanese drum or Indian chant, the songs you'll be learning will be based on a repeating pattern of beats. The most common are 4/4 time and 3/4 time. Don't worry about what those mean, but understand what they sound like. 4/4 time usually has an emphasis on ONE and THree. The emphasis on ONE is stronger. So it's ONE two THRee four, ONE two THRee four. 3/4 has an emphasis on one and is also called waltz time because it's what waltzes are written in. ONE two three, ONE two three. If you don't know when to count a note, that's why you need a metronome. So get one.
Now you've got the metronome and you can mostly get between the chords (don't worry, everyone blows chord changes now and then). Now play the song with the metronome very, very slow. Don't try and do what the original artist does. Just play on the beats and the chords. You'll add the chikaboom to boom chikaboom soon. For now, just do the boom. When you can do clean chord changes in time, and increase the time a little over a while, THEN start adding in additional strums to get the sound you want at the pace you want.
The first song could take you four months or more.
In time, you'll be like Russell who heard a song in the morning and recorded it that afternoon. In time.
As you learn chords and chord changes, they'll apply to other songs and you won't have to go through this long of a process, because your fingers will already know what to do.
Good luck, and have fun.
- Zurf
Granted B chord amnesty by King of the Mutants (Long live the king).
If it comes from the heart and you add a few beers... it'll be awesome! - Mekidsmom
When in doubt ... hats. - B.G. Dude