MySQL - How to structure DB for millions rows

I have a table of trades with 2.5M rows.

I try to run this query:

 SELECT id, price FROM trade
 order by price DESC
 limit 30

this query takes about 3 seconds.

I tried to create an index for the columns that I order by but the order is generic and can be on other columns (quantity, date, etc...).

What can I do to improve the execution time of order 2.5M rows without indexes?