If you have to tug or pull firmly, the berries will still be too sour to eat raw. Avoid collecting from roadsides. Berries collected near roads can contain high levels of hydrocarbons and other chemicals. Avoid putting your berries in plastic bags, they ferment very quickly on a hot day, and may be bad when you get home. Lightweight pants and long-sleeved shirt will protect you from both thorns and sunburn.
Ticks love thickets.
Make sure you check your whole body carefully when you get home. Use a reputable field guide, such as Peterson's, to identify the many edible brambleberries in your area. Apple Berry Jam - Brambleberries do not gel well. The apples in this recipe provide pectin for a firmer jam. They may be left out if you prefer a softer fruit spread.