Kind of a generic question there buddy, but let's see what we can do to spice it up.
The obvious and easiest way is to, amazingly, just plant them in and pick them up from the loamy soil whenever their cycle ends, which is counted in real time hours and is different from each berry.
You could also get berries by capturing a 'mon that is currently, at the time you're battling it, carrying one and has not yet ate it.
It goes without saying that an exchanged Pokemon holding a berry would result in you receiving the berry it's holding.
Speaking of 'mons, some of them have the ability called PICK UP, which grants them the possibility of, as implied, picking up objects from the ground.
Why is this relevant? Because, in the Fire Red and Leaf Green versions, pick up would mostly results in your Pokemon holding a berry. This was changed tho and berries are no longer available via pick up in later generations.
One other way is to, if you are playing OR/AS, get a Secret Pal for your base that has the ability "Gather Berries", which would grant you a berry a day, but keep in mind that your flag level and the class and gender of the Pal have a factor in this.
Here are links where you can find more info about the ability Pick up, Secret Pals and most importantly berries.
Hope I helped!