Well it's official, I stupidly ruined a painting while varnishing with a brand new brush and it got lint ALL over my beautiful painting.
I've never actually varnished using a brush before, I used to always spray varnish. I did use liquid varnish to create some smoggy masterpieces in high school though (I really enjoyed experimenting with all mediums despite their intended purpose!)
In our current home I have no outdoor space where I can use spray varnish safely and I don't have proper ventilation to spray indoors either so liquid varnish it is!
Some tips to get you started on varnishing inside.
Make sure your piece has fully cured whether it be an oil painting, acrylic, mixed media etc.
Wipe down your piece if it's been sitting for a while to rid it of any dust or particles that you can't see, but will if you start to varnish it! (I've made this mistake too)
Make sure that your brush is clean - even if it's brand new and in a plastic case it can still be full of dust (hard lesson learned here for me folks!)
Prepare your varnish per it's instructions and begin with light layers. You don't want to make it a smoggy mess and ruin your beautiful painting.