well
this is pretty much how to build a deck.
1. You chose a deck-type, monster-type, or archtype on which your deck is going to be built. Archtype means, that there are multiple cards of that name, like Gishki, Dragunity or X-Saber.
2. When you've decided what you are going to run, for example Gishki, you start looking for cards that support the deck. In this case, we look for cards that carry Gishki in their name. You read through all their effects, and then decide what the best cards could be in the deck you intend to run. Since Gishki runs a lot on Ritual, you will search Gishki cards that support Ritual summons, like Gishki Shadow, or Vision Gishki. When you have found enough cards that support the deck through it's main build, you start looking for staples.
3. Staples are cards that are usable in pretty much every deck. Examples for staples are:
- Mystical Space Typhoon
- Dark Hole
- Heavy Storm
- Monster Reborn
- Solemn Judgment
- Solemn Warning
These are only some staples, but it's not a must in your deck. however, it usually increases a deck's power.
4. After you have staples, you look for cards that might support your deck indirectly, meaning cards that aren't created for the archtype, but created for, let's say the attribute, or the monster-type you use. In this case, a very good card in a Gidhki deck, is Salvage. Since a lot of the Gishki monster have 1500 ATK or less, Salvage runs good in that deck, because you'll be able to recycle the cards more easily.
5. Now we're gonna take a look at Extra Deck. In your Extra Deck you put Fusion, Synchro and XYZ monsters. Fusion is not used in Gishki, so we won't need that. Synchro can be used, in caase you run tuner monsters. Standard Synchro monsters are usually Black Rose Dragon, Stardust Dragon, Scrap dragon, Ally of Justice Catastor and Brionac, Dragon of the Ice Barrier. When you have your Synchro's, you can look for XYZ monsters. Gishki has a lot of level 2, level 4 and level 8 monsters. So, we look for rank 2, 4 and 8 XYZ monsters. Usually, Gachi is the only Rank 2 monster used. For rank 4 we have many choices. Once again, just read their effects, and choose the best that run in your deck. Rank 8 is barely summonable. So, we don't use them, because the odds that you'd get them on the field are way too small.
Well, with all that, you should either have a good Gishki deck, or any other good deck. And remember, if the deck doesn't run well, you can always keep looking for the problem. Is it fast enough? Can it negate the actions of the opponent enough? Do the cards work at all?
I hope that with all of this, you can build your own decks well =p
Good luck on the deckbuilding