@sven @q3k
1) Apply effective decongestant drops/spray first and wait a couple minutes for it to work, to make sure the blockage can actually be relieved somewhere (don’t get hooked on decongestants, though, use only when sick for a few days a few times per day);
2) Have a slightly hypertonic saline solution ready (e.g. ~0.5 teaspoon salt per 200 ml BOILED water (non-boiled water in the nose means brain-eating amoebas), use your taste calibrated to off-the-shelf medical IV saline solution and make it just slightly more salty, but not too salty to be alarming, one teaspoon is too much, and 1/3 teaspoon per 200 ml is isotonic and too diluted);
3) Use a nasal douche/neti pot/squeeze bottle/whatever nasal pressure washing medical device according to its instructions (very important, don’t hurt yourself);
4) When blowing the nose outwards, ALWAYS open your mouth and use minimal force, so that you don’t hurt your ears (yes, the shit can go the other direction and into the eustachian tubes, sadly).

Advanced level of (3): simply inhale the saline solution directly through one nostril from a cupped palm of your hand, while blocking the other nostril with the fingers of said palm or your other hand (which may be holding the glass with the soliton, YMMV) until the nose is clear enough, repeat on the other nostril until AGI achieved internally.

Source: lived in multiple cold wet climates.