This is a common question and many people incorrectly believe you should have tight, restrictive walking boots. This is an easy way to damage your feet, but a loose boot can be just as uncomfortable and detrimental to your walking. The simplest way to think of this is to go for snugness rather than tightness.
When trying out hiking boots for the first time, you should make an effort to go later in the day. Feet swell throughout the day and trying boots towards the evening will provide a more realistic fit after a day on the move. Find a pair in your size, and you may want to bring along some walking socks so you get a more accurate gauge for the fit due to them being thicker than normal socks. They should fit your feet well with a small amount of space at the front so your toe isn’t scrunched up.
When laced up, your foot should feel supported but there should be no point where it feels too tight as any pressure points will be a hotbed for blisters and pain. Make sure you are very comfortable before you make a decision as any uncomfortable points will be amplified over a whole day of walking.
While breaking in your boots is a part of any hiker’s routine, the boots should still be comfortable before this process. This goes for any insoles you regularly wear, which you should bring along to check the fit too.