I'll start with champagne cocktails. I like champagne cocktails because they are unfussy to make, without any stress-inducing exacting recipes and methods and one doesn't need any elaborate and expensive equipment or tools either. Better put the money you are saving into the ingredients, because cheap stuff shows -- or rather tastes. Simplicity is paramount.
Method: Just see that the glasses and ALL the ingredients are very cold. The champagne-ingredients ratio is really up to taste.
Classic: Sugarcube, some drops of Angostura Bitter. This is maybe the only cocktail that requires real champagne or at least so I think. (Lovely pink bubbles! My favourite!) It's for a reason I can not pinpoint, maybe because it's not fruity, an excellent winter drink. Campari isn't really, as some claim, an alternative.
Buck's Fizz/Mimosa: Freshly pressed orange juice to taste. Add gin and peach schnapps and you'll get a Jacuzzi, but the latter is too fussy a recipe for my idea of champagne cocktails.
Kir Royal: With Creme de Cassis. (I think it's overrated.)
Bellini: Fresh peach puree from a ripe peach. Peach schnapps won't do any harm. Avoid canned fare.
Pear Bellini: Fresh pear puree from a very ripe pear, pear schnapps .
Nelson's Blood: With Tawny Port. Brits sometimes take the opportunity to give a toast, which is very appropriate.
Black Velvet: With Stout. (Corrupts two perfectly good drinks by mixing them. Yuck!)
Champagne Cooler: Good for using various content of your bar. For example any Brandy or Cognac, or orange flavoured mixers like Curaçao Triple Sec, Cointreau or Grand Marnier.
Elderflower: Add elderflower syrup. Light and pleasant variety!
I realize that die-hard champagne lovers may think all this a sacrilege, and although it is always recommended to use the most expensive ingredients one can afford, I dare saying that the thing that can be first compromised when making champagne cocktails is
I positively hate those heavy, herbal mixers, such as Chartreuse or anything minty. Besides, I think green looks vile in a drink. And I don't even WANT to know how that awful German liqeur Jägermeister tastes when mixed with Champagne, and the same applies to Pernod. If anything, both are something for a down and out party under the bridges.
Talking about Sekt: I'm not a sparkling hock drinker (it's not so much that I don't like it, but it doesn't seem to agree with me) and when I arrived here in East Germany, I was adamant that I'd never touch the regional fare because of my snobbish West German ways and specifically because I thought that something that goes by an unspeakable name like Rotkäppchen ("Little Red Riding Hood") was bound to be crappy. Well, I was wrong. I bet it's the best price-performance ratio in the entire sparkling wine market.