Equipment

Mountains make different demands on the bike material
On a bike that you ride along on the flat without any problems, you can not necessarily ride perfect in the mountains. Of course you should have enough light gears to kick the slopes upwards. But in addition: a bike that on the flat appears to be technically perfect, appears in the mountains sometimes not quite right. The impact is different in the mountains, something creaks slightly, the chain or wheels touches something and the derailleur does not work accurate. And so forth.
A few points you do wise to pay attention. Briefly mentioned because on material is on the internet unendlessly much to find.

Gears and resistance

 

Do you have to put before you go into the hills or mountains on your backwheel a different (mountain) set with a 27, 28 or even 32 instead of 23 as the smallest sprocket? And for the crankset? Do you need to assemble a compact crankset (34-50) where you have on the flat just a double crankset (39-52)? Or do you already have a triple.
Incidentally: In the flat you would like to switch per time one tooth. Then you can peddle with the right frequency and the right power. If you ride on the flat with a mountain gearing set with large steps between the teeth, you therefore cannot find the right frequently and the ideal resistance. Maybe on the plane as the smallest opposition to take a 23?

Brakes, wheels and tires

There are different types of brakes and brake pads in combination with different rims. In addition, there is the difference between the rim brakes and disc brakes.
What is good in the flat is not per se good enough for long and steep descents.

In addition, different types of brakes, the brakes and blocks brake differently.

Customization
It is important that you can easily keep the bite levers (by 2 to 3 fingers). In case of need you don’t want to reach out to the brakeslevers. Do you have small hands, that is sometimes difficult. For some levers are auxiliary pieces that bring the lever a little closer to the steering wheel. Otherwise make the slack in the cable a bit more so you can keep the lever a little attracted without the brake already touching the rim.
A ‘scare’centimeter space in the cable is anyway handy if you’re in unexpected situations tend to react too fast rather than too slow. Before you attract the brake unnecessary and sometimes dangerous too quickly, that extra space in the cable gives you the chance to recover from the initial shock and not (hard) braking where it is not wanted.

Road tire contact: slipping
The most critical at braking is the tire-road contact. There is a big difference between tires in how much they can be braked without slipping. The most durable tires have the hardest rubber. They wear the least, go the least leak, but slip the fastest (in turns). On a wet road that is worse than on a dry road.
If you are with a group you need to know whether these differences are mutually so big that you have to take that into account.

Dosing and overreact

You try to avoid that the brakes ‘snap’, blocking the wheel. That’s a bit trickier with rim brakes than disc brakes. The right rubbers and the right space in the cable help much. Possibly you mount the brake pads slightly tapered at the rim. As a result, the brake shoes get hold of the rim not directly over the entire length of the blocks, but gradually from front to back (and especially not vice versa, then they snap even more :)).

In wet roads, you will have to brake dry the rims of rim brakes regularly in order to prevent them from taking a while before they do their job properly.

The fact that disc brakes engage harder and slow down more than rim brakes is not an advantage as long as the limiting factor is the contact between the tire and the road surface. The main advantage of disc brakes is the (easier) dispensability.

NB do not trust blindly that the material will do the job. Disc brakes are not necessarily better. It is important that your material is perfectly mounted and adjusted. And that you yourself know how to use it.

Continuous braking, heat
If you brake continuously on a descent to keep the speed that can make the wheels  very warm. Because of the heat the (inner) tube expand and may even explode. If you ride with tubes, the adhesive can be too hot and the tubes come loose. If you drive with carbon rims the carbon material can become slack and not well to stop the pressure of the tire.
Feel now and again the rim, especially of the front wheel. In frontwheel the brake brakes the hardest and therefore is the warmest. Can you hardly grasp, it is not good. Let it cool, maybe with some water from your water bottle on it.
By not continuously braking but shorter braking (and more severe) the rims are more likely to cool off during the descent. And riding, you also have beautiful the wind and cooling than standing alongside the road.

The pros ride almost always on carbon rims. But they  brake less often and long. For cyclists, it is probably wiser to ride with aluminum rims (or disc wheels).
See also: Cycling in the mountains or hills / Professionals and cyclists

Reserve Material
In the mountains the bicycle shop is often not around the corner and you do’nt want to spend your time looking for one. It is wise to take at least: repairset, reserve inner tires and outer tires,brake pads (A wet weekend in the mountains can wear a set of blocks). A chain or, in any case, a connecting link, for example a quick link. And tools, among others, inbuss keys, screwdriver, chain tool. Are you with a group, it is also useful to carry a spare wheel.
Please be aware that the components from various suppliers such as Campagnolo, Shimano and SRAM usually do not fit together. Also note whether your group is 9, 10 or 11 speed.