Hi Dubai
A target list would be helpful if you have one. Also, will you have access to a car?
Off the top of my head:
1. Friston Forest at Cuckmere haven would offer a small variety of estuary birds/waders & gulls at the mouth of the River Ouse - also a good spot for Northern Wheatear, Yellow/Pied Wagtail, Stonechat, Meadow Pipit, Little Egret, Peregrine, Hobby and possibly Merlin. Across the road from the entrance to Cuckmere Valley NR, is a Sussex Woodland Trust ie. Friston Forest: Here, easy Woodpeckers/Green/Great Spotted - I've seen Lesser Spotted here too. Also, Siskin, Common Treecreeper, Nuthatch, Firecrest, good range of Tits etc. Further along the main route (about 1m) is a fantastic Rookery!
Keep going north and there's miles of mixed habitat including meadow/deciduous and downland - good for Tree Pipit, Short-Eared Owl, Spotted Flycatcher etc etc
2. Ashdown Forest (is good if you have a car!) - Mixed habitat of Heath and Woodland - good for Dartford Warbler, Redstart, Crossbill (if your lucky), Short-eared Owl ... usual raptor species (ie. Merlin, Sparrowhawk, kestrel, Buzzard), Firecrest etc ... Head to Old Lodge NR
3. Pulborough Brooks RSPB NR & Wiggonholt Common - Mixed habitat of Woodland -(deciduous/pine), heath, meadow and water - Good for Nightjar, Woodlark, Tawny, Barn and Short-Eared Owl and usual woodland species. Small variety of waders on the Brooks.
4. West Dean Woods - in West Sussex - You may see Red Kite here, Lesser Spotted Woodpecker amongst the more unusual
The first three are mixed habitat - in summer, woodland birding in UK can be rather challenging, so you could also focus on whatever the weather/light dictates on the day.
There are more but perhaps if you Google these sites (the names should all through up some links) and Google map for directions, it would be a start.
Pm me if you want further directions/species lists for the above or more places to go