Early on in your rhythmic development you will find it very helpful to count rhythms aloud. You might feel silly doing it, but something about the physical act of vocalizing rhythms really helps you absorb them and play them accurately. Don’t be shy about counting rhythms out loud. You won't have to do it forever, but in the beginning it really helps.
Nearly every time I have a student struggling with a rhythm it clears up as soon as they count the rhythm out loud. Until they've absorbed it, often it falls apart as soon as they stop counting. Count the rhythm, absorb and master it, then set it free in your subconcious.
Traditional Rhythm Counting
Traditionally teachers teach you to count rhythms using numbers along with some other words or sounds. You would count the beat 1, 2, 3, 4, 1, 2, 3, 4, 1, and so on. In-between you would fill in the word ‘and’ for the eighth note subdivisions of each beat. A measure of eighth notes would be counted aloud, “1-and-2-and-3-and-4-and.”
Since this is how most people learn it, it’s a good idea to know it that way, too. A musician might communicate to you, “Play that B-flat on the and of 2.” That would mean to play it on the eighth note falling between beats 2 and 3.
Similarly, 16th notes are traditionally counted “1-e-and-a-2-e-and-a-3-e-and-a-4-e-and-a” and so on dividing each beat into 4 syllables.
You might discover counting rhythms this way is a little awkward. You might run out of breath. Many people teach rhythm counting another (in my opinion better) way that is less awkward.
Counting Rhythms with Nonsense Syllables
To make vocalizing rhythms more comfortable, you can assign some simpler-to-say nonsense syllables to each of the 1-e-and-a’s. I like to teach students to divide each beat into 4 syllables I made up: doom-ba-tek-ah. Naturally, you can make up your own syllables. Just be consistent and use ones that are rhythmic and easy to vocalize.
“Doom” is the beat where you'd be counting 1, 2, 3, 4. Just vocalizing the beat you’d say, “Doom-doom-doom-doom.”
“Tek” is the “and”, or eighth note, between each beat. To count all eighth notes you’d say, “Doom-tek-doom-tek-doom-tek-doom-tek.”
Finally, you can add “ba” and “ah” for the 16th notes between the “dooms” and “teks”. To count sixteenths you’d say, “Doom-ba-tek-ah-doom-ba-tek-ah-doom-ba-tek-ah-doom-ba-tek-ah.”
Practice Counting Rhythms
Find any music notation you can and count the rhythm out loud using the appropriate nonsense syllables. Don't concern yourself with speed. Focus on accuracy first. Use a metronome to pace yourself.
As you study more rhythms you’ll start to recognize their sound and feel from the nonsense syllables you learned to vocalize. You'll see this really helps with complicated and syncopated rhythms.
Count and vocalize those rhythms out loud!