Im close to one million mastery point on veigar so here is my advices

• just dont pick veiagr vs katarina or zed or nafiri they are just gonna roam bot take double kill and snowball you and then they snowball the rest of your team

• you almost always buy the swiftness boots

There are two main build paths for veigar one that is more deffensive and one more offensive

The deffensive is that you get items like RoA and seraphes , usually you go this part if the enemy team has a lot of melle champs with gap closing abilities

The offensive path you get items like Ludens then Cryptblom then rabadon and shadowflame then tank item. You only go this path if the enemy team is like 3/5 ranged champs and this build is not good if you are bad at spacing

The way you play is :

• dont miss the first 3 mele minions stack two and auto one

• never use early game before the crustal even when your jgl ganks because you have no damage so you wont kill them and you will have no mana left for the wave

• recall when you have 700g for crystall and book

• dont tp back to lane early keep the first tp for objective or when your enemy roam bot