As a guitarist your intent should be focused on playing with perfect timing.  When playing music, timing and rhythm should be foremost in your mind.  As you progress, this will come naturally; but it takes years of hard work.  Perfect practice makes perfect, so for the next drill you need a metronome or some kind of beat machine (something that plays beats to perfect timing).  I prefer playing to a beat than a metronome, as it is more fun, sounds better, and gives you good practice for playing to drums.  Set the tempo to 100 or even slower if that is too fast.  Listen to the beat and get a feel for it.  Notice each element of it; the bass drum, the snare, the high hat, etc.  Also notice when the beat starts over/repeats itself.  If your beat machine has a choice for time signatures then choose 4/4 timing.  As you advance you can explore other timings, but 4/4 is the most straight forward and easy to understand.  It is also the most common time signature in modern day popular music.

As the beat is playing, count out the tempo: 1 2 3 4.  After 4 you go back to 1.  At 1 is where the beat starts over again/repeats.  Once you have a feel for the beat, including recognizing the tempo, you can start the exercise.  The more you do this the easier it will be to recognize the tempo and structure of a beat.

Start off by choosing a chord (such as E minor) or even a simple power chord.  Play your chord at the beginning of the beat.  Each time it comes around, each time the beat starts over, you will strike your chord.  Be sure and do it perfectly at the first hit of the beat.  Once you get a feel for this, add a second chord or power chord and play it at the half way point of the beat.  So if you count your tempo as 1 2 3 4; then at 1 you will play your first chord, and at 3 you will play your second chord.  As the beat starts over you will repeat this.  Do this until you can perform it with no mistakes.  As your timing gets better, you can play more complex rhythms to different beats.  I encourage you to follow this path of growth, always aiming for perfection!