Looking for a new bike, any tips for buying a good bike?
You don't say where you are located, so it is bit hard to tell what your specific requirements might be, but you do make a distinction around 'winter riding'.  So let's assume you mean cold, perhaps treated roads, perhaps snow, perhaps ice.

For tires, while there's some tension between 'wide' and 'fast', I would suggest 32mm or wider, if they'll fit in your frame, fork, and brakes.  Something with tread if you plan on riding in the wet or on treated (gravel-covered) roads.  If you expect to encounter ice, you may want studs.

Another unknown is time of day and what the lighting conditions will be.  In my opinion the single biggest safety improvement you can make is to ensure you are visible in darkness and in low light, to drivers who are in a hurry, tired, and often distracted.  

I would recommend highly visible (hi-viz yellow and orange) clothing, many reflectors (especially moving reflectors, such as ankle bands and spoke reflectors), a bright, multi-mode, rechargeable stroboscopic rear light; a bright, constant-beam, rechargeable front light, and an auxiliary stroboscopic white front light.  There are many good choices out there.

There are also helmets with integrated safety lights available; these work well in my experience.

If you are looking for specific product recommendations I'm sure many folks can provide them.