How do I get to the march route?
Avoid taxis, Ubers, and other car services, as the streets are likely to be packed or closed off. The best way to get to Freedom Plaza is by taking the DC Metro along the Red, Blue, Orange, or Silver lines to the Metro Center stop. The Penn Quarter/Navy Memorial, L'Enfant Plaza, and Smithsonian Metro stops are all also nearby or a short walk away.
What should I wear or bring for the weather?
Comfortable shoes and warm clothing are absolutely necessary this weekend. Umbrellas won't be a bad idea either, as the forecast currently looks like a mixture of light snow and frigid rain. Temperatures are forecasted at a high of 39º F as of Thursday afternoon. If you want to bundle up and represent the cause, the march's website has a bunch of official merch, including hoodies, beanies, and more.
Definitely pack snacks and reusable water bottles (there will be water stations) to keep your endurance up. Small backpacks and bags are allowed, as are signs; the only restriction on signs in DC is the height limit of 12 feet. Do not bring weapons, and to be safe, don't bring anything that might be mistaken for a weapon; leave any knives, box cutters, scissors, or multi-tools at home. Do not bring illegal drugs, even pot. (Marijuana is legal in DC, but is crucially not legal on the federal property that the march will be moving on.)
Above all, have fun, stay safe, and be respectful. Public nonviolent protest is one of the cornerstones of American democracy, and one of the core tools that voters can leverage against those in power. That's an inspiring thing, no matter who you voted for.