Whenever we put our 12 week old on her tummy, she yelps and generally sounds uncomfortable. She looks a bit like an upturned tortoise. How can we make this more enjoyable for her?
It might sound harsh, but there's not much you can do to make it enjoyable; if you're on your belly and aren't strong enough to raise your head up yet, tummy time is not going to be fun.
However, you can limit the upset for your child by not putting her through an excessive amount - little and often is better than fewer long stints. (Advice on how long it should be varies - we had healthcare professionals telling us a newborn (at 1-2 weeks) should be doing 5 minutes at a time, and others telling us this was a ridiculous amount of time for a child.)
Long term, you want to put up with a certain amount of noise and discomfort, because your child needs to use her neck muscles to develop strength in them. Keep it consistent - try and do it at similar times in her daily routine, and prioritise lots of short bursts rather than longer ones. We'd put her on her back as soon as she'd managed to move from looking to the left to the right, and tell her how well she was doing, but beyond that and being present, there isn't much else to do.
Tummy time is complicated at that age, but it's definitely necessary. Don't expect anything to work perfectly, but also don't do it past the point of her being frustrated; helping her enjoy it is critical to getting longer periods in later. At 12 weeks you likely can only do a short bit at a time (10-15 minutes at most, I'd expect more like 3-5 minutes usually).
One of the most useful things is a tummy time mat with interesting things on it. The two we used for our two little ones had various parts that had crinkly bits, mirrors, textures, etc., on different parts, was fairly cushy, and had a mobile like part above it. This helped our children get used to the mat on their backs, so when we flipped them over they weren't too upset. One I got for my nephew had a piano part, where if he hit it with his hand or foot it made music - this was a huge hit. Basically anything that gets a visual, aural, tactile response will be helpful here.
Lots of stimulation by you is also helpful. Make tummy time one of the times you have a lot of mommy or daddy and baby interactions. Don't expect tummy time to be a put baby down and do the dishes time - talk to baby, stroke and touch baby, tickle baby, etc. The more positive stimulation, the better, as baby will then be more interested in the future.
In a few weeks or a month, maybe around 4-5 months, you can start putting toys around baby. Probably at 3 months this won't yet really be helpful, but you can try now if you want (particularly if baby has very strong neck control). Don't put them out of reach, but at the edge of reach; out of reach is for 6-8 months when crawling begins to be possible.
Change baby's position often at first. Don't just have tummy time. Have a minute of tummy time, then sit baby up (probably this will be assisted sitting at this age), then hold baby on your lap. Change those positions more frequently than baby gets annoyed about any one of them.
Most of all, don't give up. Tummy time is important, and it may be one of the first times you will have to really work on something that doesn't work at first. Stick to it; it's worth it!
In our case, what helped was: