[Sparko]

There are a lot of parts that can wear or get damaged in the drivetrain. As stated, your syncros could be a problem, you could also have a bent or otherwise damaged shift fork. Does it grind when your shifting into first, that could be a faulty clutch/hydraulic component, or does it feel like the gear is blocked off? When you shift it into first and then start rolling does it ever pop back out of gear? Did this start suddenly or has it been problematic at an increasing rate/severity? How many miles are on the car? Miles would help to know if you're at a point where something specific has typically worn to a problematic point. What kind of troubleshooting and maintenance has been done already to the drivetrain?

You wouldn't walk into an electrical shop and say "my lights don't work, what could it be?" and then ask again after they ask if you changed your bulbs or plugged the lights in without providing more information.