If you have many people that abandon shopping carts in your online store, may exist many reasons for this. One could be the fact on how people make purchase decisions. Initially they start from emotional of point and transition logical reasoning, if someone initiate checkout period add effort to complete order will have to be kept at minimum. If you remove all elements that cause distraction that kind of distractions you could have a smooth checkout process that could lead to higher conversion ratese.
Clean Checkout Process
In modern theme design, you can see frequently long footers with many menus and a newsletter subscription form. In checkout page there is not need for such need footers with such many info. Here a possible outcome, for a message in the newsletter copy, "subscribe now you will have 5% discount on your first order", this type of copy in checkout could cause a general disruption.
Final total price
A clear view on final price is important because every potential buyer would know precisely what he will pay. Despite the choice of payment method, shipping destination or discount codes to calculate total price accurately is very important.
There are many cases that somebody use a coupon code and there is no proper integration with the payment method so when you redirected to payment provider in screen appears the total price different thatn the the cart without the discount. This pure quality integrations can prevent many users from completing order and also lower trust factor on your online store.
Customer support and refund policy
When you have a clear defined return and refund policy this could make more comfortable users to make purchases in online stores. Specially items like clothes that you cannot have a clear idea on quality from a picture. For example someone could order a jacket that could have a good quality, but was not suitable for winter, it has to be possible to return and taking your money back easily and without problems. Also in e-commerce business refund policy is obligatory by local laws.
Multiple payment methods
Having a wide variety of payment methods do not allow customers to think twice on how will pay. A wide range of payment methods such as credit card, cash on delivery, paypal, wire transfer is important. Do not let customers think twice about about type payment methods and delivery options, Also if a user is already a customer at checkout page, he should see first, payment methods his preferred method. A good personalized experience could remove a lot of friction and obstacles.