How often to water

Sow seeds into damp soil and you shouldn't need to water till they germinate. If the compost does get very dry, then sit the tray in water for 10 mins then remove. Once they are bigger, water from beneath when compost is dry to an inch or so down. Once planted out into the soil, drenching every 3 days is better than a spot of water twice a day - the roots are encouraged to grow deep to find water making stronger plants.

Absolutely, I second all that Shirl says. It is more often an error to overwater than to underwater; it is the classic mistake of a keen, over-anxious gardener.
(We've all been there, at times some of us still are there !)
Decide what they need first of all based upon the soil when they are at seedling stage, and then as they get bigger outside by the state of the leaves. But like children, if you mollycoddle them too much they will always demand it, and be less vigorous.

I've been there- overwatered my herb pot last year and killed of my herb seedlings
I overwatered my chilli plant as well over winter but i've stopped watering it so much now and it's doing much better.

The seeds have been planted out as per the instructions on the packet - Mange Tout and also Pak Choi.

The Runner beans that went into pots in the green house last wednesday, have already started poking out of the soil, with little green heads.

Ive attached a pic of the Mangetout going in, and how it looked this morning after watering

So what happens if it rains then, its going to be well watered then. Is once a day more suitable then, unless its been an overly hot day.

Problem is about a foot or so below the ground it gets abit sandy, as around my area there used to be a sand and gravel pit, so it will drain pretty easy

Also, I use a watering can to water them, not hose pipe

I suppose the best thing to do is to check the soil with your hands, if it's still quite moist then it probably doesn't need watering but if it feels dry then give it a water.

I'm no expert though but i only water my stuff based on how the soil feels
(I push my finger into the soil so i can feel how moist it is under the top layer)

Very tidy, looks good !
In persistently wet weather seedlings do tend to have a higher mortality rate, and struggle to reach the point beyond which they are no longer merely struggling to survive but are actually thriving. This is partly because of low UV levels - some plants cope better with this than others, there are 3 different ways of photosynthesising - but also because rain bring fungal spores with it. Raindrops splashing back off the soil will coat the leaves with spores lying on the soil surface; once on the leaf the fungi come to life and attack through the leaf pores.
The good news mcbronco is that the sandy soil you have makes this a bit less likely, fungi don't like sandy soil so much because it doesn't stay moist. (They need the right temp and humidity for the spores to wake up.) The bad news of course is that nutrients will leach faster out of your soil as the water drains out rapidly.
How often to water is a question rather like how long is a piece of string. It depends on how the plant is doing, and what the forecast is, will you be on holiday... There is one rule of thumb I go by. If you press a piece of newspaper to the soil and it comes away damp, don't water.
As long as the top six inches or so of soil is rich in humus, the plants will do okay, up to a point. Obviously, in very hot weather or a drought, then you have problems. Then I would think maybe of buried soaker hoses, which are very effective in the economical use of water. (But a pain if you forget they are there - mark them well. ) You can get these quite cheaply at Lidl's sometimes, for example. Watering cans are a lot more efficient than standard hoses at directing the water to the plants you want, rather than watering every weed seed lying waiting with a dry mouth !
Long term, the best answer is to improve your soil, by adding humus and mulching it to keep the moisture in once you have sown and watered.
Personally, my allotment is sandy loam, and that is one reason why I use raised beds, with lots of newspapers and leaf mould etc in the bottoms.
Knowing what to do in the garden is a science. Knowing when to do it is an art.

The thing I always try to remember is that just because it looks dry on top doesn't mean it is dry underneath! Sometimes only the surface dries out and it is still moist underneath. If the surface looks dry, stick your finger down an inch or two and check out the soil underneath. Only water if it is dry underneath.
Good luck.

Yes, that tends to happen when you get capping. (The little grains bind together as they dry, forming a moistureproof skin that inhibits germination. ) I suppose that is a dust mulch Demeter - it keeps the moisture in underneath, or stops it from penetrating from above. Apparently in Asia they use stones as mulch.
The old saying goes, a mulch is anything that preserves the status quo, so you don't put it on dry soil, and when the soil becomes dry you must scrape it away from round the plants before watering and replacing.