If possible, it would be best to go to school to collect it tomorrow.
If you can, you should go to school to collect it tomorrow.
丁寧な言い方：
If possible,it would be best to go to school to collect it tomorrow.
できれば、明日学校に取りに行った方が良い。
普通の言い方：
If you can, you should go to school to collect it tomorrow.
できれば(あなたは）明日学校に取りに行った方が良いよ。
"go" は学校の先生が話す場合は "come"「来て」にした方が良いです。
先生（親に話す場合）：
If possible,it would be best to come to school to collect it tomorrow.
先生（生徒に話す場合）：
If you can, you should come to school to collect it tomorrow.
アイルランド 
