The whole point of shuffling a deck of cards is to randomise the order of them. For the best results, you need to give the deck at least seven basic rifle shuffles.
This video from the Numberphile YouTube channel features statistics and mathematics professor Persi Diaconis of Stanford University explaining why you need at least seven shuffles. Of course, the shuffles need to be the standard riffle shuffle and not the overhand shuffle (that type takes about 10,000 shuffles to reach the same level of randomisation).
Smooshing, the process of spreading the cards around the table and mixing them together, can be effective as well, but you need to do it for about a minute. If you'd like to read more about the maths, you can check out the original study here. Good shuffling requires practice, but it's not too hard to pick up.