Praia do Guincho is well-known for its wind- and kitesurfing conditions due to its location close to Cabo da Roca (the most western point of continental Europe). However, when the wind calms down, Guincho is actually also one of the best beach breaks of the region. It picks up lots of swell, is consistent and attracts local crowd from the Lisbon area.
The waves are suitable for beginners on the smaller days, but will get very powerful when the size increases. Usually there is a good lefthander on the south side of Guincho beach and an a-frame more towards the middle. This surf spot can work with all tides, depending on the position of the sand banks. But low to mid tide is normally your best bet. Watch out for the rocks in the middle of the beach!
If Guincho is too crowded, it might be worth to check the smaller bay just south of Guincho called Praia da Cresmina.