Peter: When I was taught music theory in school, my teacher told me 3/4 time meant 3 beats to a bar and the 4 represented the 1/4 note got 1 beat. The important thing is that the 1st beat was pronounced (strong). and the 2nd beat was soft The 3rd beat was stronger then the 2nd but not as loud as the 1st. Now to play a strong beat on the guitar, you have to strum downwards, it only makes sence. soft beats are strumed upwards.
The next step is to know how to count each bar, and because it is in 3/4 time you count to 3. Therefore if you have to count 4 bars you would count them like this. 1,2,3 - 2,2,3 - 3,2,3 - 4,2,3. Now keeping that in mind, count in your head a few bars, and enficise the 1st beat, also the 3rd beat a little less. 1=LOUD 2=SOFT 3=MEDIUM It should sound like a train going down the track. The most Important part is that struming comes naturally with practice. Just listen to the train and strum down up down.
The last point is, that even though there is 3 beats to a bar, each beat can last, say 1 second. You can split that beat (strum) in half or quarters or eights. thats how you get 1/2 notes 1/4notes etc. Therefore you can strum as many times as you like, as long as you can fit them into a bar. So start off by struming down and make your own combination of up and down strokes to equal 3 seconds. then repeat it all over for the second bar, then the third.etc. hope this helps you. e-mail me if you get stuck email@example.com