The first tip I want to give you is to play something fun. Go through your cards, every single one, and look at them. Find a few that sound or look awesome. For standard, this is most likely going to be a big creature, though it could be anything. Pick a few of these cards. This will be the foundation of your deck, the card or cards you build around.
With this decided, acknowledge their colors, or lack there of. Maybe its a colorless creature like
Desolation Twin. Maybe its a white enchantment like
Starfield of Nyx. Or a very aggressive red critter like Reckless Bushwacker. Whatever card you choose to build around, our goal is now to make that card work more efficiently. For most cases, this is going to involve casting this card, either at the earliest possible time, or in a way that sets you up to then win the game.
So, as an example deck, lets say you choose
Desolation Twin as your build around card. This creature is a 10/10 for ten mana, AND when he enters the battlefield, you put a 10/10 token into play. 10 is a very, very big number in Magic, both in casting cost, and his power and toughness. Because he costs so much mana, you probably won't be casting it very often; assuming you play a land every single turn for ten turns, you still can't put this powerful creature on the table until your tenth turn. As such, you'll turn to ramping spells and abilities.
Ramp is a term to describe acceleration in Magic, and almost exclusively is used to refer to mana. To build around
Desolation Twin, you'd want to choose creatures that generate mana, such as
Beastcaller Savant,
Hedron Crawler, and
Warden of Geometries, as well as spells that allow you to put lands into play, cards like
Explosive Vegetation and
Nissa's Pilgrimage. Each of these cards will allow you to generate mana more quickly than an opponent playing a different style deck. Using these supporting cards, you can deploy your
Desolation Twin far earlier; around turn seven or eight with a perfect draw.
However, there's a
catch. While throwing every ramp spell imaginable into your deck seems like the fastest and most ideal way to deploy this deck, doing so will put you in an extremely disadvantaged position, because you'd only have four pay off cards. You need additional cards, spells and creatures that will protect you, and weaken or attack your opponents and their creatures.
By adding cards that kill creatures, commonly called removal or answers in Magic slang, one can protect their own life total from enemy creatures, and ensure they have more time to set up their own victory condition. The hypothetical deck idea we're discussing here however has a problem with this. Green as colors go has the weakest removal spells in the entire color pie. As such, we'll be adding a second color.
As mentioned by other uses, the five colors have their own unique strengths and weaknesses. Green is famous for its mana ramp capabilities, its giant and usually undercosted creatures, its mana producing creatures, its
weakness against flying creatures, its lack of removal, and specialty at destroying enchantments and artifacts. By supplementing one color with another, you overlap the strengths of each color, and
hide some of the weaknesses.
Red: cheap removal, cheap hasty creatures, a focus on
aggression and
hostility, extremely strong versus artifacts but helpless against enchantments, weak versus big creatures, and vulnerable to running out of resources. Red is the go to color for a player who wants their opponents life total at zero by turn four. It is a common splash choice to access cheap removal spells, though it typically has a poor game plan against creatures with high toughness.
Blue: counter spells, bounce spells, tap spells, card draw spells, blue is excellent at stalling the game and forcing its opponent to play by its rules. It is vulnerable to enchantments and artifacts. Its is typically also vulnerable to enemy creatures, as its removal is second weakest only to green. Blue is a color that is paired with others more than any other, and often plays a defensive game, up until it locks down the situation.
Black: powerful removal spells at varying cost, hand disruption, strong graveyard interaction capabilities, a "power at any cost" mentality and a
complete disregard for its own life total. Black is very weak against enchantments and artifacts, but is extremely powerful against creatures. Black decks are capable of attacking aggressively, defending their position, or picking apart their opponent until they can move in for the kill. Black is capability of working alongside any other color, and supplementing its
weakness with its powerful removal spells.
White: a synergistic color capable of gaining life, attacking enchantments and sometimes artifacts, it has a healthy variety of creatures, ranging from small weenies as seen in red, to bigger creatures found in green. White is notorious for deploying undercosted cheap creatures, and also for its powerful board wipe effects. White also has relevant removal, though all of it typically with some kind of limitation or
weakness. White's biggest
weakness is it often runs out of cards in hand as it deploys it cheap creatures, and is then at the mercy of top decking.
Back to the deck construction, mixing your colors with any of the other four is acceptable and capable of being effective. I personally prefer either blue or black. Blue in particular grants counterspells, and black offers potent removal. Either is acceptable. So lets say you add in some black cards for removal;
Ultimate Price,
Ruinous Path,
Grasp of Darkness, etc etc all shore up a
weakness of your primary color, green, and enable you to actually protect yourself while you wait for your
Desolation Twin to be cast.
As for the card quantity, a good rule of thumb is 24, 24, and 12, which is to say 24 lands, 24 creatures and 12 spells. This is by no means a hard and fast rule, but rather a guideline to start building with. In the case of this deck, its far more likely to be more mixed. Because the deck contains mana ramping spells, additional lands are beneficial. Your creatures are focused on producing mana, so having too many of these is not advisable. Lastly, the deck will basically demand additional spells greater in quantity than 12, as you have so many you need to cast.
Tl, dr; find a card you like. Build a deck around it using cards you think will support it.
I hope this helps you! Welcome to Magic!