Aside from the tips that have already been mentioned it's not an easy thing to do. It's just the more experience you have the less likely you are to end up with a streaky mess. As withered preacher mentioned you should be applying thin coats with cloths. I like mutton cloth for this job. Any brush application will be more likely to overload the surface in some areas, there are foam brushes which some people like.
You are not applying much at all but slowly darkening the wood in as even a manner as possible. Make sure you don't go over your work once it's started to dry until it's fully dry that way you should be able to take an entire coat off if it goes tits up by using a wet cloth (before it's dried). Don't let it dry if you think it looks streaky. Normally it drys very quickly. If you are watering the dye down to make it easier to work with it will take longer to dry and it needs to be very well mixed. I found wetting the surface made it worse, that might just be my technique though.
It's then equally difficult to know when you should apply the varnish especially if you don't have any test areas as it will change the depth of colour.
Sometimes you tend to judge the results too critically as well. I'm sure there are a lot of not so even professional jobs if you shine a very bright light on them. Just bear in mind it's a craft, you can't always avoid the human element with a hand polish, sometimes it still ends happily :)
Aside from the tips that have already been mentioned it's not an easy thing to do. It's just the more experience you have the less likely you are to end up with a streaky mess. As withered preacher mentioned you should be applying thin coats with cloths. I like mutton cloth for this job. Any brush application will be more likely to overload the surface in some areas, there are foam brushes which some people like.
You are not applying much at all but slowly darkening the wood in as even a manner as possible. Make sure you don't go over your work once it's started to dry until it's fully dry that way you should be able to take an entire coat off if it goes tits up by using a wet cloth (before it's dried). Don't let it dry if you think it looks streaky. Normally it drys very quickly. If you are watering the dye down to make it easier to work with it will take longer to dry and it needs to be very well mixed. I found wetting the surface made it worse, that might just be my technique though.
It's then equally difficult to know when you should apply the varnish especially if you don't have any test areas as it will change the depth of colour.
Sometimes you tend to judge the results too critically as well. I'm sure there are a lot of not so even professional jobs if you shine a very bright light on them. Just bear in mind it's a craft, you can't always avoid the human element with a hand polish, sometimes it still ends happily :)